Add -fprofile-sample-use to Clang's driver.

This adds a new option -fprofile-sample-use=filename to Clang. It
tells the driver to schedule the SampleProfileLoader pass and passes
on the name of the profile file to use.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@194567 91177308-0d34-0410-b5e6-96231b3b80d8