[ARM] Add hardware build attributes in assembler

This passes an option to the ARM assembly parser to emit build
attributes for the hardware selected by command line options, when
assembling an assembly file.

This is not enabled for C/C++, as this would result in duplicate build
attribute directives being emitted in each inline assembly block, when
emitting assembly.

This also adds an option to allow disabling this behaviour for assembly
files, for users who were relying on the old behaviour.

Differential revision: https://reviews.llvm.org/D31813

llvm-svn: 300550