[PATCH xserver] configure.ac: Keep environment CFLAGS when testing

[Emil Velikov]

On 23 March 2016 at 04:47, Alexandre Courbot <acourbot at nvidia.com> wrote:
> DRI2 detection could fail if configure is invoked with a sysroot passed
> as CFLAGS. Ideally configure should invoke gcc with the sysroot argument
> passed to the configure script, but for some reason this is not done by
> AC_COMPILE_IFELSE.
>
> Fix this by ensuring CFLAGS are preserved when checking for stuff.
>
> Signed-off-by: Alexandre Courbot <acourbot at nvidia.com>
Nice one Alexandre. In practise one should honour the user provided
CFLAGS regardless of what they are needed for.
Props to going through and fixing all the cases !

Reviewed-by: Emil Velikov <emil.velikov at collabora.com>

-Emil