i965: Avoid blending with destination alpha when RB format has no alpha bits

The hardware does not support a render target without an alpha channel.
So when the user creates a render buffer with no alpha channel, there actually
is storage available for alpha internally. It requires special care to
avoid these unwanted alpha bits from causing any problems.

Specifically, when blending, and when the blend factors would read the
destination alpha values, this commit coerces the blend factors to instead be
either 0 or 1 as appropriate.

A similar fix was made for pre-gen6 hardware in commit eadd9b8e and this
commit shares the fixup function written by Ian then.

This commit the following es3conform test:

	rgb8_rgba8_rgb

As well as the following piglit (sub) tests:

	EXT_framebuffer_object/fbo-blending-formats/3
	EXT_framebuffer_object/fbo-blending-formats/GL_RGB
	EXT_framebuffer_object/fbo-blending-formats/GL_RGB8

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
libgl-xlib: link with -lrt

Fixes a runtime error:

glxgears: symbol lookup error: /home/brian/mesa/lib/gallium/libGL.so.1: undefined symbol: clock_gettime

v2: use $(CLOCK_LIB) and $(PTHREAD_LIBS) per Andreas Boll.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>
st/mesa: add some simple buffer/draw debug code

Reviewed-by: José Fonseca <jfonseca@vmware.com>
util: add new primitive types to pipe_prim_names[] array

Reviewed-by: Jose Fonseca <jfonseca@vmware.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.
configure: Build src/gtest at first.