FYI: maint: build: do not enable c++ warnings on 0 when nullptr is not supported.

[Akim Demaille]

Installed in maint.  There remains an error to address before
the beta.

From 7e3510e6dd3baa34fcb985173befdafbbf3569a5 Mon Sep 17 00:00:00 2001
From: Akim Demaille <address@hidden>
Date: Wed, 9 May 2012 11:20:18 +0200
Subject: [PATCH 2/2] build: do not enable c++ warnings on 0 when nullptr is
 not supported.

* configure.ac (WARN_CXXFLAGS): Enable -Wzero-as-null-pointer-constant
only when nullptr is supported..
---
 configure.ac |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 9395568..6a75d7b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -70,7 +70,7 @@ if test "$enable_gcc_warnings" = yes; then
     -Wcast-qual -Wformat -Wpointer-arith -Wwrite-strings'
   warn_c='-Wbad-function-cast -Wmissing-declarations -Wmissing-prototypes
     -Wshadow -Wstrict-prototypes'
-  warn_cxx='-Wnoexcept -Wzero-as-null-pointer-constant'
+  warn_cxx='-Wnoexcept'
   AC_LANG_PUSH([C])
   for i in $warn_common $warn_c;
   do
@@ -87,6 +87,8 @@ if test "$enable_gcc_warnings" = yes; then
   do
     gl_WARN_ADD([$i], [WARN_CXXFLAGS])
   done
+  gl_WARN_ADD([ -Wzero-as-null-pointer-constant], [WARN_CXXFLAGS],
+              [AC_LANG_PROGRAM([], [nullptr])])
   gl_WARN_ADD([-Werror], [WERROR_CXXFLAGS])
   # Warnings for the test suite only.
   gl_WARN_ADD([-Wundef], [WARN_CXXFLAGS_TEST])
-- 
1.7.10.1