When skipping building the module for a private framework module,
LangOpts.CurrentModule isn't enough for implict modules builds; for
instance, in case a private module is built while building a public one,
LangOpts.CurrentModule doesn't reflect the -fmodule-name being passed
down, but instead the module name which triggered the build.
Store the actual -fmodule-name in LangOpts.ModuleName and actually
check a name was provided during compiler invocation in order to
skip building the private module.
rdar://problem/38434694
llvm-svn: 328053
Bruno Cardoso Lopes