Added support to Platform to indicate (1) whether the
current platform supports Clang modules, and (2) what
options to pass to Clang so it can load those Clang
modules.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@223431 91177308-0d34-0410-b5e6-96231b3b80d8