build: Fix the documented default value of --with-gallium-drivers

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
gallium/svga: Make sure -std=gnu99 is set.

This is a work-around until configure.ac stops touching CFLAGS.

Reviewed-by: Matt Turner <mattst88@gmail.com>
egl/wayland: Pull color buffers from dri2_surf->color_buffers pool

We used to keep the color buffers in the dri_buffers array and
swap __DRI_BUFFER_BACK_LEFT and __DRI_BUFFER_FRONT_LEFT around there
and swap third_buffer in in case we needed to triple buffer.  That
gets a little fidgety with all the swaps, so lets use the
color_buffers pool like the gbm platform does.  We track the color buffers,
their corresponding wl_buffer and locked status here and just plug
a free one into dri2_surf->buffers when we need to.

This is a nice clean-up in itself, but it also sets us up to track
buffer age in the color_buffers structs.

Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
egl/wayland: Implement EGL_EXT_buffer_age

Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
radeon, clover: Make it compile on LLVM >= r171366.
configure.ac: Save user {C,CXX}FLAGS and append them at end.

This way the user has the privilege of last decision and so the option to build an optimized debug build again.
Suppress clang's warnings about unused CFLAGS and CXXFLAGS.
gallium/auxiliary: Build libgallium shared.
Drop last parts of compatibility for the old Mesa build system.
mapi: Build libglapi always shared.
mesa: Build libmesa shared.
Install all internal shared libs to $(libdir)/mesa-$VERSION.
Makefile.am: s:-no-undefined:-Wl,--no-undefined to make it work.
gallium/drivers: Build libs -shared.
i915: Conditionally build an i915g driver instead of two i915 drivers.