improve compatibility with GCC: when generating the ".d" filename to use

and the filename has multiple .'s in it, use the last.  For example, "foo.bar.cpp"
should produce "foo.bar.d" not "foo.d".  Patch by Johan Boule in PR8391


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@123576 91177308-0d34-0410-b5e6-96231b3b80d8