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.
Clang should warn only about unused CFLAGS and CXXFLAGS on debug builds.
tests: AM_CPPFLAGS must include $(top_srcdir) instead of $(top_builddir).
gtest: Build it only for 'make check'.
radeon, clover: Make it compile on LLVM >= r171366.
r200: Fix probable thinko in r200EmitArrays

Effectively this path would always assert.  Move the break statement to
the (probable) intended place.

Note: This is a candidate for the stable branches.

Signed-off-by: Adam Jackson <ajax@redhat.com>
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.