BaseTools ARM: add CLANG35 support

BaseTools ARM: add CLANG35 support

This extends the existing CLANG35 toolchain definition with support for
building for the ARM architecture. In order to be able to reuse the existing
ARM GCC definitions as much as possible, the following changes have been
made to the existing ARM GCC support:
- the -mapcs option has been removed; it is a no-op under Thumb (our default)
  and we use AAPCS (-mabi=aapcs) anyway
- the -mword-relocations option has been moved from GCC_ARM_CC_FLAGS to
  the GCC4x specific option: CLANG does not support it, and uses '-mllvm
  -marm-use-movt=0' instead.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19284 6f19259b-4bc3-4df7-8a09-765794883524