Replace also-emit-llvm with save-temps.

The also-emit-llvm option only supported getting the IR before optimizations.
This patch replaces it with a more generic save-temps option that saves the IR
both before and after optimizations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220885 91177308-0d34-0410-b5e6-96231b3b80d8