Publish Soong configuration to Make variables

For configuration like TARGET_GLOBAL_CFLAGS, it would be good to have
Make and Soong use the same values. This change adds an interface for
packages like cc to verify the current value of make variables match the
Soong equivalents, and once they're satisfied with the results, remove
the make definition and use the value from Soong.

The cc implementation exports a few variables currently that I expect to
match between both implementations in all cases. It also checks
{CLANG,}{HOST,TARGET}_GLOBAL_{C,LD}FLAGS, which should be mostly similar
between make and soong now.

Bug: 23566674
Change-Id: Idc8582ef31ace11a8baefcf525c3683f08a573aa
3 files changed