Makefile: provide CFLAGS for command line override.

Avoid assign to CFLAGS in Makefile.
Rename BASIC_CFLAGS to COMMON_CFLAGS.
Use PKG_CFLAGS to store external package related cflags.

V4: As point out by Luc, sparse-llvm.sc is missing the
$(LLVM_CFLAGS).

Signed-off-by: Christopher Li <sparse@chrisli.org>
Acked-by: Jeff Layton <jlayton@kernel.org>
1 file changed