i915g: Stop calling draw_prepare_shader_outputs

It's not useful on i915g since we don't support primid. Fixes
piglit point tests on i915g.
i915g: Implement writemask fixup

The fixup code emulates non-BGRA render targets by adding an
extra instruction at the end of fragment shaders to swizzle the
output. To do this, we also swizzle the blend function. However
an oversight until now was that the writemask wasn't getting
swizzled. This patch fixes that which fixes a bunch of piglit
tests.
Move nv30, nv50 and nvc0 to nouveau.
ilo: -I$(top_srcdir)/src/mesa/drivers/dri/i965
Suppress clang's warnings about unused CFLAGS and CXXFLAGS.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
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.
radeon: Build libllvmradeon the right way.

Better build system integration for:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=91a160b
http://cgit.freedesktop.org/mesa/mesa/commit/?id=5b2855b
gallium/targets: Make use of prebuilt libdricommon.la.
Drop support for --enable-static / --disable-shared.
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.
glx: Get rid of libglx.la.
gbm: Get rid of libgbm_dri.la.
i915: Conditionally build an i915g driver instead of two i915 drivers.
gallium/auxiliary/draw/draw_decompose_tmp.h: Fix clang warnings.