Make sure the math library is included when building with shared libr…

…aries.

configure

@@ -723,6 +723,7 @@ SHELL'
 ac_subst_files=''
 ac_user_opts='
 enable_option_checking
+enable_shared
 enable_pam
 enable_debug
 enable_maintainer
@@ -1359,6 +1360,7 @@ Optional Features:
   --disable-option-checking  ignore unrecognized --enable/--with options
   --disable-FEATURE       do not include FEATURE (same as --enable-FEATURE=no)
   --enable-FEATURE[=ARG]  include FEATURE [ARG=yes]
+  --disable-shared        do not install shared library
   --enable-libpam         use libpam for authentication, default=auto
   --enable-debug          turn on debugging, default=no
   --enable-maintainer     turn on maintainer mode, default=no
@@ -3893,6 +3895,20 @@ fi
 
 
 
+# Check whether --enable-shared was given.
+if test ${enable_shared+y}
+then :
+  enableval=$enable_shared;
+fi
+
+if test x$enable_shared != xno
+then :
+
+    LIBS="$LIBS -lm"
+
+fi
+
+
 # Check whether --enable-pam was given.
 if test ${enable_pam+y}
 then :

configure.ac

@@ -111,6 +111,13 @@ dnl Check for pkg-config, which is used for some other tests later on...
 AC_PATH_TOOL([PKGCONFIG], [pkg-config])
 
 
+dnl Math library...
+AC_ARG_ENABLE([shared], AS_HELP_STRING([--disable-shared], [do not install shared library]))
+AS_IF([test x$enable_shared != xno], [
+    LIBS="$LIBS -lm"
+])
+
+
 dnl PAM support...
 AC_ARG_ENABLE([pam], AS_HELP_STRING([--enable-libpam], [use libpam for authentication, default=auto]))