[libvirt] [PATCH] build: fix configure detection of if_bridge.h on RHEL 6

[Daniel P. Berrange]

On Tue, Aug 06, 2013 at 02:41:55PM -0600, Eric Blake wrote:
> A fresh checkout on a RHEL 6 machine with these packages:
> kernel-headers-2.6.32-405.el6.x86_64
> glibc-2.12-1.128.el6.x86_64
> failed to configure with this message:
> checking for linux/if_bridge.h... no
> configure: error: You must install kernel-headers in order to compile libvirt with QEMU or LXC support
> 
> Digging in config.log, we see that the problem is identical to
> what we fixed earlier in commit d12c2811:
> 
> configure:98831: checking for linux/if_bridge.h
> configure:98853: gcc -std=gnu99 -c -g -O2  conftest.c >&5
> In file included from /usr/include/linux/if_bridge.h:17,
>                  from conftest.c:559:
> /usr/include/linux/in6.h:31: error: redefinition of 'struct in6_addr'
> /usr/include/linux/in6.h:48: error: redefinition of 'struct sockaddr_in6'
> /usr/include/linux/in6.h:56: error: redefinition of 'struct ipv6_mreq'
> configure:98860: $? = 1
> 
> I had not hit it earlier because I was using incremental builds,
> where config.cache had shielded me from the kernel-headers breakage.
> 
> * configure.ac (if_bridge.h): Avoid conflicting type definitions.
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> Pushing under the build-breaker rule, and backporting to v1.1.1-maint

This change breaks configure on any Fedora install I have, so I've
had to revert it in master, since broken Fedora is more of a show
stopper than broken RHEL6.

Daniel
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