gallivm: Improve debug output (V2)

gallivm: Improve debug output (V2)

Improve debug output from gallivm_compile_module and
lp_build_create_jit_compiler_for_module, printing the
-mcpu and -mattr options passed to LLC.

V2: enclose MAttrs debug_printf block and llc -mcpu debug_printf
in "if (gallivm_debug & <flags>)..."

Signed-off-by: Ben Crocker <bcrocker@redhat.com>
Cc: 12.0 13.0 17.0 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com> (v2)
[Emil Velikov: rebase]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>