When loading a module that involves submodules (e.g., std.vector),

When loading a module that involves submodules (e.g., std.vector),
check whether the named submodules themselves are actually
valid, and drill down to the named submodule (although we don't do
anything with it yet). Perform typo correction on the submodule names
when possible.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@145477 91177308-0d34-0410-b5e6-96231b3b80d8