Revert "Backport atomic job locking from ksh 93v- beta" (52067c3)

That patch broke the build on Cygwin, where gcc apparently doesn't
have the required atomic addition/subtraction compiler builtins.
The build fails at link time with those functions not found.

As far as I know, ksh was actually working fine (after @JohnoKing's
gcc workaround in c258a04), so I'll just revert this for now. If a
need for it is demonstrated later, we'll have to add a feature test
or find some other way to get it working on Cygwin.

src/cmd/ksh93/include/jobs.h

@@ -33,7 +33,6 @@
 #   include	<signal.h>
 #endif /* !SIGINT */
 #include	"FEATURE/options"
-#include	<aso.h>
 
 #undef JOBS
 #if defined(SIGCLD) && !defined(SIGCHLD)
@@ -126,13 +125,16 @@ extern struct jobs job;
 #define vmbusy()	0
 #endif
 
-#define job_lock()	asoincint(&job.in_critical)
+#define job_lock()	(job.in_critical++)
 #define job_unlock()	\
 	do { \
-		int	_sig; \
-		if (asogetint(&job.in_critical) == 1 && (_sig = job.savesig) && !vmbusy()) \
-		    job_reap(_sig); \
-		asodecint(&job.in_critical); \
+		int	sig; \
+		if (!--job.in_critical && (sig = job.savesig)) \
+		{ \
+			if (!job.in_critical++ && !vmbusy()) \
+				job_reap(sig); \
+			job.in_critical--; \
+		} \
 	} while(0)
 
 extern const char	e_jobusage[];

src/cmd/ksh93/sh/jobs.c

@@ -1891,8 +1891,14 @@ static int job_chksave(register pid_t pid)
 
 void *job_subsave(void)
 {
-	struct back_save *bp = new_of(struct back_save,0);
+	/*
+	 * We must make a lock first before doing anything else,
+	 * otherwise GCC will remove the job locking mechanism
+	 * as a result of compiler optimization.
+	 */
 	job_lock();
+
+	struct back_save *bp = new_of(struct back_save,0);
 	*bp = bck;
 	bp->prev = bck.prev;
 	bck.count = 0;