1 files changed, 24 insertions, 2 deletions

diff --git a/gl/m4/visibility.m4 b/gl/m4/visibility.m4
index 6d3f9c9..077c476 100644
--- a/gl/m4/visibility.m4
+++ b/gl/m4/visibility.m4
@@ -1,4 +1,4 @@
-# visibility.m4 serial 2 (gettext-0.18)
+# visibility.m4 serial 3 (gettext-0.18)
 dnl Copyright (C) 2005, 2008-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -26,15 +26,37 @@ AC_DEFUN([gl_VISIBILITY],
   CFLAG_VISIBILITY=
   HAVE_VISIBILITY=0
   if test -n "$GCC"; then
+    dnl First, check whether -Werror can be added to the command line, or
+    dnl whether it leads to an error because of some other option that the
+    dnl user has put into $CC $CFLAGS $CPPFLAGS.
+    AC_MSG_CHECKING([whether the -Werror option is usable])
+    AC_CACHE_VAL([gl_cv_cc_vis_werror], [
+      gl_save_CFLAGS="$CFLAGS"
+      CFLAGS="$CFLAGS -Werror"
+      AC_TRY_COMPILE([], [],
+        [gl_cv_cc_vis_werror=yes],
+        [gl_cv_cc_vis_werror=no])
+      CFLAGS="$gl_save_CFLAGS"])
+    AC_MSG_RESULT([$gl_cv_cc_vis_werror])
+    dnl Now check whether visibility declarations are supported.
     AC_MSG_CHECKING([for simple visibility declarations])
     AC_CACHE_VAL([gl_cv_cc_visibility], [
       gl_save_CFLAGS="$CFLAGS"
       CFLAGS="$CFLAGS -fvisibility=hidden"
+      dnl We use the option -Werror and a function dummyfunc, because on some
+      dnl platforms (Cygwin 1.7) the use of -fvisibility triggers a warning
+      dnl "visibility attribute not supported in this configuration; ignored"
+      dnl at the first function definition in every compilation unit, and we
+      dnl don't want to use the option in this case.
+      if test $gl_cv_cc_vis_werror = yes; then
+        CFLAGS="$CFLAGS -Werror"
+      fi
       AC_TRY_COMPILE(
         [extern __attribute__((__visibility__("hidden"))) int hiddenvar;
          extern __attribute__((__visibility__("default"))) int exportedvar;
          extern __attribute__((__visibility__("hidden"))) int hiddenfunc (void);
-         extern __attribute__((__visibility__("default"))) int exportedfunc (void);],
+         extern __attribute__((__visibility__("default"))) int exportedfunc (void);
+         void dummyfunc (void) {}],
         [],
         [gl_cv_cc_visibility=yes],
         [gl_cv_cc_visibility=no])