Teach Clang to recognize and ignore GCC's -fdiagnostics-show-location
flag. We should probably wire at least some variants of this up to our
actual diagnostics engine, but I'm leaving that for someone else. This
fixes the builds of packages which hard code something here, at least
including libstdc++ itself.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193318 91177308-0d34-0410-b5e6-96231b3b80d8
Teach Clang to accept and ignore -f[no-]implicit-templates.

This GCC flag is useful when you want to control whether implicit
template instantiation occurs at the commandline level. Clang doesn't
currently support such controls, but technically *always* implicitly
instantiating (what Clang does, and what every other compiler still in
use does by default) is valid behavior even under
-fno-implicit-templates, it just may be slow and very wasteful. If
people really want this, we can try to implement it, but I don't have an
actual use.

This should help fix the build of libstdc++ with Clang, its build system
uses this flag.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193319 91177308-0d34-0410-b5e6-96231b3b80d8