Fix build on systems that require -lm (re: 4edfa45)

@JohnoKing reports:
> Ksh now fails to build on the specified operating systems unless
> -lm is added to LDFLAGS when invoking bin/package. Failing to
> manually add -lm results in missing symbol errors for functions
> such as frexpl.

The build is confirmed to fail upon linking the libast version of
mamake on NetBSD, DragonflyBSD and Illumos.

Analysis: The root cause of the problem is that the probe in
src/lib/libast/Mamfile, lines 276-301, fails to add a '-lm' line to
ast.req. This probe is designed to figure out is math functions are
dependent on libm. It compiles/links src/lib/libast/port/astmath.c
for a number of values of the macro N, trying a different math
function each time. If any one of them fails without '-lm' but
succeeds with '-lm', the '-lm' is added to libast's dependencies as
processed by mamake.

The problem is that the probe function calls in astmath.c get
optimised out because their values, and hence the results, are
known at compile time -- so linking succeeds where it should fail.
When compiling with -O0 to disable optimisation, the probe works
correctly, -lm is added to ast.req (so mamake includes it in the
mam_libast MAM variable), and the build succeeds on NetBSD without
any problem.

So, the fix is for astmath.c to work around compiler optimisation.

This fixes an old problem in the build system. With the root cause
fixed, we are now also able to remove a bunch of -lm workarounds.

src/lib/libast/port/astmath.c:
- Replace fixed 0 values with rand() calls to avoid probe call
  results being known at compile time.

src/lib/libast/Mamfile:
- For some reason, the N=7 astmath.c case was not tried; add it.
- Tweaks to error out early in case of failure.

src/cmd/builtin/Mamfile,
src/cmd/builtin/features/pty:
- Remove -lm workarounds. (re: d79a34b, dd0d03b, d3cd4cf)

src/cmd/ksh93/Mamfile:
- Instead of passing `-lm` directly, properly use ${mam_libm} as
  this is set by 'bind -lm'. (re: 2b27f63)

Resolves: #715

src/cmd/builtin/Mamfile

@@ -112,7 +112,7 @@ make install virtual
 			exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -I${PACKAGE_ast_INCLUDE} -DERROR_CATALOG=\""builtin"\" -DCMD_STANDALONE=b_pty -c pty.c
 		done pty.o
 		bind -lutil dontcare
-		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o pty pty.o ${mam_libutil} ${mam_libast} -lm ${mam_libcmd}
+		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o pty pty.o ${mam_libutil} ${mam_libast} ${mam_libcmd}
 	done pty
 	make ${INSTALLROOT}/bin
 		exec - mkdir -p ${INSTALLROOT}/bin

src/cmd/builtin/features/pty

@@ -11,8 +11,7 @@ lib	openpty,_getpty,ptsname -lutil
 lib	grantpt,unlockpt,posix_openpt stdlib.h
 lib	cfmakeraw termios.h
 
-# try once with -lm, once without
-tst - -lm - - output{
+tst output{
 	#include	<fcntl.h>
 	#if _lib_ptsname
 	#include	<stdlib.h>
@@ -51,11 +50,8 @@ tst - -lm - - output{
 		return 0;
 	}
 }end fail{
-	case ${_features_pty_TRIEDONCE-no} in
-	no)	_features_pty_TRIEDONCE=yes ;;
-	*)	echo "$0: Output block failed to compile. Export IFFEFLAGS=-d1 to debug." >&2
-		exit 1 ;;
-	esac
+	echo "$0: Output block failed to compile. Export IFFEFLAGS=-d1 to debug." >&2
+	exit 1
 }end
 
 extern	_getpty		char*		(int*, int, mode_t, int)

src/cmd/ksh93/Mamfile

@@ -1031,7 +1031,7 @@ make install virtual
 						make features/math.sh
 							prev data/math.tab implicit
 						done features/math.sh
-						exec - iffe ${IFFEFLAGS} -v -c "${CC} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS}" ref ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -I${PACKAGE_ast_INCLUDE} -I${INSTALLROOT}/include ${mam_libdll} ${mam_libcmd} ${mam_libast} ${mam_libm} ${mam_libnsl} -lm : run features/math.sh ${PACKAGEROOT}/src/cmd/ksh93/data/math.tab
+						exec - iffe ${IFFEFLAGS} -v -c "${CC} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS}" ref ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -I${PACKAGE_ast_INCLUDE} -I${INSTALLROOT}/include ${mam_libdll} ${mam_libcmd} ${mam_libast} ${mam_libm} ${mam_libnsl} : run features/math.sh ${PACKAGEROOT}/src/cmd/ksh93/data/math.tab
 						prev ${PACKAGE_ast_INCLUDE}/ast_standards.h implicit
 						make ${INSTALLROOT}/src/lib/libast/FEATURE/float implicit
 							prev ${INSTALLROOT}/src/lib/libast/FEATURE/standards implicit
@@ -1163,7 +1163,7 @@ make install virtual
 			exec - (ranlib libshell.a) >/dev/null 2>&1 || true
 		done libshell.a
 		bind -lshell
-		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o ksh pmain.o ${mam_libshell} ${mam_libnsl} ${mam_libast} -lm
+		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o ksh pmain.o ${mam_libshell} ${mam_libnsl} ${mam_libast} ${mam_libm}
 	done ksh
 	make shcomp
 		make shcomp.o
@@ -1179,7 +1179,7 @@ make install virtual
 			exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I. -Iinclude -I${PACKAGE_ast_INCLUDE} -DSH_DICT=${SH_DICT} -D_API_ast=20100309 -DERROR_CONTEXT_T=Error_context_t -c sh/shcomp.c
 		done shcomp.o
 		prev ksh
-		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o shcomp shcomp.o ${mam_libshell} ${mam_libnsl} ${mam_libast} -lm
+		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L.} ${mam_cc_L+-L${INSTALLROOT}/lib} -o shcomp shcomp.o ${mam_libshell} ${mam_libnsl} ${mam_libast} ${mam_libm}
 	done shcomp
 	make shell virtual
 		prev libshell.a

src/lib/libast/Mamfile

@@ -272,6 +272,7 @@ make install virtual
 				note * generate initial ast.req
 				note *
 				prev ${INSTALLROOT}/bin/mkreq
+				exec - set -o errexit
 				exec - mkreq ${CC} ${mam_cc_FLAGS} ${CCFLAGS} : ${LDFLAGS} : ast iconv w
 				note *
 				note * some systems move -lc routines to -lm; see astmath.c for details
@@ -281,21 +282,24 @@ make install virtual
 						prev std/endian.h
 					done port/astmath.c
 					exec - X=1
-					exec - for N in 1 2 3 4 5 6 8
+					exec - for N in 1 2 3 4 5 6 7 8
 					exec - do	if	${CC} ${CCLDFLAGS} -DN=$N -DIS ${mam_cc_FLAGS} ${CCFLAGS} -I. -Istd ${LDFLAGS} -o astmath.exe port/astmath.c 2>/dev/null
 					exec -		then	: implicit math function N=$N :
 					exec -		elif	${CC} ${CCLDFLAGS} -DN=$N -DIS ${mam_cc_FLAGS} ${CCFLAGS} -I. -Istd ${LDFLAGS} -o astmath.exe port/astmath.c -lm 2>/dev/null
 					exec -		then	: math function N=$N requires -lm :
 					exec -			X=0
 					exec -			break
+					exec -		else	: ERROR: astmath.c fails to compile or link, even with -lm :
+					exec -			exit 1
 					exec -		fi
 					exec - done
 					exec - ${STDRM} -rf astmath.exe*
 					exec - echo $X > astmath.out
 				done astmath.out
 				prev FEATURE/aso
 				exec - sed -e '/^#define _REQ_/!d' -e 's/#define _REQ_\([a-z0-9_]*\).*/ -l\1/' FEATURE/aso >> ast.req
-				exec - case $(${STDCAT} astmath.out) in
+				exec - read no_libm_needed <astmath.out
+				exec - case $no_libm_needed in
 				exec - 0)	echo ' -lm' >> ast.req ;;
 				exec - *)	touch ast.req ;;
 				exec - esac
@@ -4989,6 +4993,7 @@ make install virtual
 			exec - ${CC} ${mam_cc_FLAGS} ${CCFLAGS} -I${INSTALLROOT}/include/ast -D_PACKAGE_ast -c ${PACKAGEROOT}/src/cmd/INIT/mamake.c
 		done mamake.o
 		bind -last
+		exec - set -o errexit
 		exec - ${CC} ${CCLDFLAGS} ${mam_cc_FLAGS} ${CCFLAGS} ${LDFLAGS} ${mam_cc_L+-L${INSTALLROOT}/lib} -o mamake mamake.o ${mam_libast}
 		note *
 		note * We purposely do not have a make target of ${INSTALLROOT}/bin/mamake here;

src/lib/libast/port/astmath.c

@@ -2,7 +2,7 @@
 *                                                                      *
 *               This software is part of the ast package               *
 *          Copyright (c) 1985-2011 AT&T Intellectual Property          *
-*          Copyright (c) 2020-2023 Contributors to ksh 93u+m           *
+*          Copyright (c) 2020-2024 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 2.0                  *
 *                                                                      *
@@ -20,27 +20,33 @@
 /*
  * used to test if -last requires -lm
  *
- *	arch		-last			-lm
- *	----		-----			---
- *	linux.sparc	sfdlen,sfputd		frexp,ldexp	
+ * This program is compiled and linked from a probe script in libast/Mamfile
+ * but never actually run. It is only used to check if linking succeeds
+ * without or with -lm.
+ *
+ * For that test to work correctly, we must work around compiler optimization.
+ * The rand() calls are to stop the result from being considered known at
+ * compile time, which would cause modern compilers to optimize out the probe
+ * calls, which would in turn cause linking to succeed where it shouldn't.
  */
 
 #if N >= 8
 #define _ISOC99_SOURCE	1
 #endif
 
+#include <stdlib.h>
 #include <math.h>
 
 int
 main(void)
 {
 #if N & 1
-	long double	value = 0;
+	long double	value = rand();
 #else
-	double		value = 0;
+	double		value = rand();
 #endif
 #if N < 5
-	int		exp = 0;
+	int		exp = rand();
 #endif
 
 #if N == 1