[4.0] 2001b7e DEVELOPER_CFLAGS: - use -fstack-protector only if both compiler and linker support it - use -Wno-missing-field-initializers vs -Wno-extra depending on compiler support - -Wno-pointer-sign only if compiler supports it - add -Wno-address to avoid "the address of ‘buf’ will never be NULL" warning in cache_backend_cfg.c (and in other places where REPLACE() is used with local buf variable)

[Nils Goroll]

commit 2001b7efbb114a9c4de5184c87e3c31fc4bee14e
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Wed Mar 19 19:57:34 2014 +0100

    DEVELOPER_CFLAGS:
    - use -fstack-protector only if both compiler and linker support it
    - use -Wno-missing-field-initializers vs -Wno-extra depending on compiler support
    - -Wno-pointer-sign only if compiler supports it
    - add -Wno-address to avoid "the address of ‘buf’ will never be NULL" warning in
      cache_backend_cfg.c (and in other places where REPLACE() is used with local
      buf variable)

diff --git a/configure.ac b/configure.ac
index 55c62ab..e2a0b98 100644
--- a/configure.ac
+++ b/configure.ac
@@ -470,7 +470,6 @@ DEVELOPER_CFLAGS=" \
 	-Wall \
 	-Wno-format-y2k \
 	-W \
-	-Wno-unused-parameter \
 	-Wstrict-prototypes \
 	-Wmissing-prototypes \
 	-Wpointer-arith \
@@ -483,10 +482,9 @@ DEVELOPER_CFLAGS=" \
 	-Wcast-align \
 	-Wchar-subscripts \
 	-Wnested-externs \
-	-Wno-pointer-sign \
 	-Wextra \
-	-Wno-missing-field-initializers \
 	-Wno-sign-compare \
+	-Wno-address \
 "
 
 # These are not compliable yet
@@ -505,7 +503,10 @@ AC_ARG_ENABLE(stack-protector,
        [enable_stack_protector=yes])
 
 if test "x$enable_stack_protector" != "xno"; then
-       DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -fstack-protector"
+	AX_CHECK_COMPILE_FLAG([-fstack-protector],
+		AX_CHECK_LINK_FLAG([-fstack-protector],
+			[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -fstack-protector"], [], []),
+		[], [])
 fi
 
 # --enable-developer-warnings
@@ -515,6 +516,16 @@ AC_ARG_ENABLE(developer-warnings,
 	[enable_developer_warnings=no])
 
 if test "x$enable_developer_warnings" != "xno"; then
+	# compiler flags not available on gcc3
+	AX_CHECK_COMPILE_FLAG([-Wno-pointer-sign],
+		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-pointer-sign"], [], [])
+	# no known way to specifically disabling missing-field-initializers warnings
+	# keeping the rest of Wextra
+	AX_CHECK_COMPILE_FLAG([-Wno-missing-field-initializers],
+		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-missing-field-initializers"],
+		[DEVELOPER_CFLAGS="${DEVELOPER_CFLAGS} -Wno-extra"],
+		[])
+
 	CFLAGS="${CFLAGS} ${DEVELOPER_CFLAGS}"
 	OCFLAGS="${OCFLAGS} ${DEVELOPER_CFLAGS}"
 fi
diff --git a/m4/ax_check_link_flag.m4 b/m4/ax_check_link_flag.m4
new file mode 100644
index 0000000..db899dd
--- /dev/null
+++ b/m4/ax_check_link_flag.m4
@@ -0,0 +1,73 @@
+# ===========================================================================
+#    http://www.gnu.org/software/autoconf-archive/ax_check_link_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CHECK_LINK_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+#   Check whether the given FLAG works with the linker or gives an error.
+#   (Warnings, however, are ignored)
+#
+#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+#   success/failure.
+#
+#   If EXTRA-FLAGS is defined, it is added to the linker's default flags
+#   when the check is done.  The check is thus made with the flags: "LDFLAGS
+#   EXTRA-FLAGS FLAG".  This can for example be used to force the linker to
+#   issue an error when a bad flag is given.
+#
+#   INPUT gives an alternative input source to AC_LINK_IFELSE.
+#
+#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
+#   macro in sync with AX_CHECK_{PREPROC,COMPILE}_FLAG.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Guido U. Draheim <guidod at gmx.de>
+#   Copyright (c) 2011 Maarten Bosmans <mkbosmans at gmail.com>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 3
+
+AC_DEFUN([AX_CHECK_LINK_FLAG],
+[AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_ldflags_$4_$1])dnl
+AC_CACHE_CHECK([whether the linker accepts $1], CACHEVAR, [
+  ax_check_save_flags=$LDFLAGS
+  LDFLAGS="$LDFLAGS $4 $1"
+  AC_LINK_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+    [AS_VAR_SET(CACHEVAR,[yes])],
+    [AS_VAR_SET(CACHEVAR,[no])])
+  LDFLAGS=$ax_check_save_flags])
+AS_IF([test x"AS_VAR_GET(CACHEVAR)" = xyes],
+  [m4_default([$2], :)],
+  [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_LINK_FLAGS