[AArch64][clang] Pass cpu/arch information to assembler for AArch64.

Summary:
Pass Cpu/Arch options to assembler for AArch64 with no-integrated-as.
This fixes PR20019.

Reviewers: richard.barton.arm, kristof.beyls, rengolin

Reviewed By: rengolin

Subscribers: srhines, pirama, aemerson, rengolin, cfe-commits

Differential Revision: https://reviews.llvm.org/D32132

llvm-svn: 300571