vdpau,xvmc: Add install-data-hooks to remove unneccessary symlinks.

libvdpau_*.so.1 and libXvMC*.so libs are dlopened by wrappers.
So only those libs should be installed.
glx: Get rid of libglx.la.
gbm: Get rid of libgbm_dri.la.
i915: Conditionally build an i915g driver instead of two i915 drivers.
freedreno: Make print_sequence a macro to fix clang.
freedreno: One Makefile.am with a Makefile.sources is enough.
clover: Force gcc and g++ to fix clang builds.
gallium/auxiliary/draw/draw_decompose_tmp.h: Fix clang warnings.
More scan-build fixes.