Move functionality for handling module maps as inputs from the -emit-module

Move functionality for handling module maps as inputs from the -emit-module
action to the general FrontendAction infrastructure.

This permits applying -E, -ast-dump, -fsyntax-only, and so on to a module map
compilation. (The -E form is not currently especially useful yet as there's no
good way to take the output and use it to actually build a module.)

In order to support this, -cc1 now accepts -x <lang>-module-map in all cases
where it accepts -x <lang> for a language we can parse (not ir/ast). And for
uniformity, we also accept -x <lang>-header for all such languages (we used
to reject for cuda and renderscript), and -x <lang>-cpp-output for all such
languages (we used to reject for c, cl, and renderscript).

(None of these new alternatives are accepted by the driver yet, so no
user-visible changes.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@301610 91177308-0d34-0410-b5e6-96231b3b80d8