a modifier for a header declarartion, e.g.,
umbrella header "headername"
Collapse the umbrella-handling code in the parser into the
header-handling code, so we don't duplicate the header-search logic.
llvm-svn: 146159
the module is described in one of the module maps in a search path or
in a subdirectory off the search path that has the same name as the
module we're looking for.
llvm-svn: 144433