PR 17421: Implemented -save-temps={obj|cwd} option

-save-temps=cwd is equivalent to -save-temps
-save-temps=obj saves temporary file in the same directory as output

This helps to avoid clobbering of temp files in case of parallel
compilation with -save-temps of the files that have the same name
but located in different directories.

Patch by Artem Belevich

Reviewed By: rnk

Differential Revision: http://reviews.llvm.org/D7304

llvm-svn: 227886