Use AX_ADD_FORTIFY_SOURCE

Include a workaround for newer versions of MingW

configure.ac

@@ -217,10 +217,7 @@ AC_C_VARARRAYS
 
 AC_CHECK_DEFINE([__wasi__], [WASI="yes"], [])
 
-AC_CHECK_DEFINE([_FORTIFY_SOURCE], [], [
-  AX_CHECK_COMPILE_FLAG([-D_FORTIFY_SOURCE=2],
-    [CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"])
-])
+AX_ADD_FORTIFY_SOURCE
 
 AX_CHECK_COMPILE_FLAG([-fvisibility=hidden],
   [CFLAGS="$CFLAGS -fvisibility=hidden"])

m4/ax_add_fortify_source.m4

@@ -0,0 +1,74 @@
+# ===========================================================================
+#  https://www.gnu.org/software/autoconf-archive/ax_add_fortify_source.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_ADD_FORTIFY_SOURCE
+#
+# DESCRIPTION
+#
+#   Check whether -D_FORTIFY_SOURCE=2 can be added to CPPFLAGS without macro
+#   redefinition warnings or linker errors. Some distributions (such as
+#   Gentoo Linux) enable _FORTIFY_SOURCE globally in their compilers,
+#   leading to unnecessary warnings in the form of
+#
+#     <command-line>:0:0: error: "_FORTIFY_SOURCE" redefined [-Werror]
+#     <built-in>: note: this is the location of the previous definition
+#
+#   which is a problem if -Werror is enabled. This macro checks whether
+#   _FORTIFY_SOURCE is already defined, and if not, adds -D_FORTIFY_SOURCE=2
+#   to CPPFLAGS.
+#
+#   Newer mingw-w64 msys2 package comes with a bug in
+#   headers-git-7.0.0.5546.d200317d-1. It broke -D_FORTIFY_SOURCE
+#   support, and would need -lssp or -fstack-protector.  See
+#   https://github.com/msys2/MINGW-packages/issues/5803. Try to
+#   actually link it.
+#
+# LICENSE
+#
+#   Copyright (c) 2017 David Seifert <soap@gentoo.org>
+#   Copyright (c) 2019 Reini Urban <rurban@cpan.org>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved.  This file is offered as-is, without any
+#   warranty.
+
+#serial 3
+
+AC_DEFUN([AX_ADD_FORTIFY_SOURCE],[
+    AC_MSG_CHECKING([whether to add -D_FORTIFY_SOURCE=2 to CPPFLAGS])
+    AC_LINK_IFELSE([
+        AC_LANG_PROGRAM([],
+            [[
+                #ifndef _FORTIFY_SOURCE
+                    return 0;
+                #else
+                    this_is_an_error;
+                #endif
+            ]]
+        )],
+        AC_LINK_IFELSE([
+            AC_LANG_SOURCE([[
+                #define _FORTIFY_SOURCE 2
+                #include <string.h>
+                int main() {
+                    const char *s = " ";
+                    strcpy(s, "x");
+                    return strlen(s)-1;
+                }
+              ]]
+            )],
+            [
+              AC_MSG_RESULT([yes])
+              CPPFLAGS="$CPPFLAGS -D_FORTIFY_SOURCE=2"
+            ], [
+              AC_MSG_RESULT([no])
+            ],
+        ),
+        [
+            AC_MSG_RESULT([no])
+    ])
+])