Properly pass through the PIC mode to the integrated assembler when

doing assembly-only, and unify the Driver's PIC argument parsing.

On a few architectures, parsing of assembly files annoyingly depends
on whether PIC is enabled or not. This was handled for external 'as'
already (passing -KPIC), but was missed for calls to the standalone
internal assembler.

The integrated-as.s test needed to be modified to not expect
-fsanitize=address to be unused, as now fsanitize *IS* used for
assembly, since -fsanitize=memory can sometimes imply -fPIE, which the
assembler needs to know (gack!!).

Differential Revision: http://reviews.llvm.org/D11845

llvm-svn: 245447