ArmPkg/ArmGic: Removed 'GCC' toolchain to build assembly files

ARMCC6 toolchain (LLVM based) understands the GNU assembly language.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>



git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16343 6f19259b-4bc3-4df7-8a09-765794883524