Fix ACL_CHECK_ADD_COMPILE_FLAGS to work with clang

Some compilers (e.g., clang) only issue a warning for
unsupported options unless an additional flag such
as -Werror is used to convert the warning to an error.

The behaviour is unchanged when using gcc as it either
errors or ignores unknown options whether or not -Werror
is present.

Signed-off-by: Selva Nair <selva.nair@gmail.com>
Acked-by: David Sommerseth <davids@openvpn.net>
Message-Id: <1574183023-6136-1-git-send-email-selva.nair@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg19170.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

diff --git a/configure.ac b/configure.ac
index 807804e5fcdd514137bb4e4a530298630551bfee..a47e0a06ce92e655d37c018273cc303f460662c9 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -1275,11 +1275,14 @@ if test "${enable_pkcs11}" = "yes"; then
        )
 fi
 
+# When testing a compiler option, we add -Werror to force
+# an error when the option is unsupported. This is not
+# required for gcc, but some compilers such as clang needs it.
 AC_DEFUN([ACL_CHECK_ADD_COMPILE_FLAGS], [
     old_cflags="$CFLAGS"
-    CFLAGS="$1 $CFLAGS"
-    AC_MSG_CHECKING([whether the compiler acceppts $1])
-    AC_COMPILE_IFELSE([AC_LANG_PROGRAM()], [AC_MSG_RESULT([yes])],
+    CFLAGS="$1 -Werror $CFLAGS"
+    AC_MSG_CHECKING([whether the compiler accepts $1])
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM()], [AC_MSG_RESULT([yes])]; CFLAGS="$1 $old_cflags",
         [AC_MSG_RESULT([no]); CFLAGS="$old_cflags"])]
 )