git: Fix various makefile flags

git: Fix various makefile flags

We need to pass CFLAGS and LDFLAGS to the makefile correctly so we
need to list them as part of EXTRA_OEMAKE.

We also have a problem where git hardlinks binaries in bindir with
those in its libexecdir. If we change the RPATH in one of them, it
breaks the other. We therefore set the no cross dir hardlinking flag
git already has for this kind of issue. This ensures the RPATHS for
the git-core binaries works correctly. Its pure luck this has
sometimes worked so far.

(From OE-Core rev: 64c6ae6a69215b659b82c67e238bc0fbc09a3eab)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>