Keep track of modules that have failed to build. If we encounter an

Keep track of modules that have failed to build. If we encounter an
import of that module elsewhere, don't try to build the module again:
it won't work, and the experience is quite dreadful. We track this
information somewhat globally, shared among all of the related
CompilerInvocations used to build modules on-the-fly, so that a
particular Clang instance will only try to build a given module once.

Fixes <rdar://problem/12552849>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168961 91177308-0d34-0410-b5e6-96231b3b80d8