targets/dri-r600: Force c++ linker in all cases

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=59282
target/dri-swrast: fix for nonstandard LLVM prefix

Include LLVM_LDFLAGS when building with LLVM.  Fixes the following build
errors:
  CXXLD  swrast_dri.la
  /usr/bin/ld: cannot find -lLLVMR600CodeGen
  /usr/bin/ld: cannot find -lLLVMR600Desc
  /usr/bin/ld: cannot find -lLLVMR600Info
  /usr/bin/ld: cannot find -lLLVMR600AsmPrinter

Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>
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>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
tests: AM_CPPFLAGS must include $(top_srcdir) instead of $(top_builddir).

Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>
gtest: Build it only for 'make check'.

Reviewed-by: Andreas Boll <andreas.boll.dev@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
xmlpool: Fix out-of-tree builds.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
radeon, clover: Make it compile on LLVM >= r171366.
gallium/svga: Make sure -std=gnu99 is set.
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.