[libvirt] [libvirt-glib] build: allow building with newer glibc-headers and -O0

[Daniel P. Berrange]

On Wed, Jun 13, 2012 at 05:02:44PM +0200, Christophe Fergeau wrote:
> Commit log and autoconf snippet written by Eric Blake for libvirt.
> 
> glibc 2.15 (on Fedora 17) coupled with explicit disabling of
> optimization during development dies a painful death:
> 
> In file included from /usr/include/limits.h:27:0,
>                  from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/include/limits.h:169,.
>                  from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/include/syslimits.h:7,
>                  from /usr/lib/gcc/x86_64-redhat-linux/4.7.0/include/limits.h:34,
>                  from util/bitmap.c:26:
> /usr/include/features.h:314:4: error: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Werror=cpp]
> cc1: all warnings being treated as errors
> 
> Work around this by only conditionally defining _FORTIFY_SOURCE,
> in the case where glibc can actually use it.  The trick is using
> AH_VERBATIM instead of AC_DEFINE.
> 
> * m4/virt-compile-warnings.m4 (LIBOSINFO_COMPILE_WARNINGS): Squelch
> _FORTIFY_SOURCE when needed to avoid glibc #warnings.
> ---
>  m4/virt-compile-warnings.m4 |    9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

ACK

Regards,
Daniel
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