BaseTools AARCH64: add separate GCC build rule for XIP objects

BaseTools AARCH64: add separate GCC build rule for XIP objects

This introduces a special .c to .obj build rule for GCC/AARCH64 that
takes into account additional compiler flags that have been specified
via *_*_*_CC_XIPFLAGS. These will be passed after (and in addition to)
the ordinary CC_FLAGS.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19637 6f19259b-4bc3-4df7-8a09-765794883524