fixup freeimage test for macOS

configure.ac

@@ -19,31 +19,40 @@ AC_CANONICAL_BUILD
 AC_PROG_LIBTOOL
 AM_PROG_CC_C_O
 
-#
-# check for libfreeimage
-#
-case "${host}" in
-	*-mingw32*)
-		WIN_FREEIMAGE_LIBS=-lws2_32
-	;;
+case "$host" in
+   *-*-mingw*)
+      LIBS="$LIBS -lws2_32"
+      ;;
+
+esac
+
+case "$host" in
+   *-apple-darwin*)
+      STDCPP_LIBS="-lc++"
+      ;;
+
+   *)
+      STDCPP_LIBS="-lstdc++"
+      ;;
+
 esac
 
 AC_CHECK_HEADER([FreeImage.h])
 
 AC_MSG_CHECKING([for libfreeimage])
 save_LIBS="$LIBS"
-LIBS="$LIBS -lfreeimage ${WIN_FREEIMAGE_LIBS} -lstdc++ -lm"
+LIBS="-lfreeimage ${LIBS} ${STDCPP_LIBS} -lm"
 AC_LINK_IFELSE(
-	[AC_LANG_PROGRAM([[#include <FreeImage.h>]],
-	[[FreeImage_DeInitialise()]])],
-	[freeimage_result=yes],
-	[freeimage_result=no])
+        [AC_LANG_PROGRAM([[#include <FreeImage.h>]],
+        [[FreeImage_DeInitialise()]])],
+        [freeimage_result=yes],
+        [freeimage_result=no])
 AC_MSG_RESULT([$freeimage_result])
 LIBS="$save_LIBS"
 if test "x$freeimage_result" = "xyes"; then
-	FREEIMAGE_LIBS="-lfreeimage ${WIN_FREEIMAGE_LIBS} -lstdc++ -lm"
+        FREEIMAGE_LIBS="-lfreeimage ${STDCPP_LIBS} -lm"
 else
-	 AC_MSG_ERROR(['libfreeimage' not found])
+         AC_MSG_ERROR(['libfreeimage' not found])
 fi
 AC_SUBST([FREEIMAGE_LIBS], [${FREEIMAGE_LIBS}])