Merge r278393 and r278395.

LLVM/Clang 3.8 is directly usable as a cross compiler for CloudABI/i686.
In 3.9rc1 there are a couple of regressions in the driver that cause it
to be less usable:

- PIE was enabled unconditionally, even though it's only available for
  x86-64 and aarch64.
- Some inline assembly fails to build, due to a shortage of registers,
  as frame pointers are not omitted.

Both these changes are fairly low risk (read: they don't affect other
targets), so go ahead and merge them into 3.9, so we can use an
unmodified compiler on all architectures.

llvm-svn: 278605