When generating the clang crash diagnostic script, strip out the -D, -F, and -I

flags.  We have preprocessed source, so we don't need these.

No test case as it's fairly difficult to make the compiler crash on demand.  I'll
patiently wait for Ben to tell me how to do this in 2 lines of code.  :)
rdar://11283560

llvm-svn: 155180