Remove unused argument.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@177293 91177308-0d34-0410-b5e6-96231b3b80d8
Refactor a bit of duplicated code to useIntegratedAs.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@177299 91177308-0d34-0410-b5e6-96231b3b80d8
Inline ShouldUseIntegratedAssembler and move the documentation to
useIntegratedAs.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@177300 91177308-0d34-0410-b5e6-96231b3b80d8