Revert "Recover better from an incompatible .pcm file being provided by -fmodule...

Revert "Recover better from an incompatible .pcm file being provided by -fmodule-file=. We try to include the headers of the module textually in this case, still enforcing the modules semantic rules. In order to make that work, we need to still track that we're entering and leaving the module. Also, if the module was also marked as unavailable (perhaps because it was missing a file), we shouldn't mark the module unavailable -- we don't need the module to be complete if we're going to enter it textually."

This reverts commit r288449.

I believe that this is currently faulty wrt. modules being imported
inside namespaces. Adding these lines to the new test:

  namespace n {
  #include "foo.h"
  }

Makes it break with

  fatal error: import of module 'M' appears within namespace 'n'

However, I believe it should fail with

  error: redundant #include of module 'M' appears within namespace 'n'

I have tracked this down to us now inserting a tok::annot_module_begin
instead of a tok::annot_module_include in
Preprocessor::HandleIncludeDirective() and then later in
Parser::parseMisplacedModuleImport(), we hit the code path for
tok::annot_module_begin, which doesn't set FromInclude of
checkModuleImportContext to true (thus leading to the "wrong"
diagnostic).

llvm-svn: 288626