[PATCH] Fix "modular" import when we find the header in the current directory

[Daniel Jasper]

  Ok. The "problem" is that the -fmodules-decluse creates an error on the transitive build steps when actually building XC and XD, which the modules under test depend on.

  I have temporarily circumvented this in r197021 by letting the declare-use tests only checks modules without actively building them (and their transitive dependencies). So you should now be able to commit this without changing the test/Modules/Inputs/declare-use/module.map.

  I think that we'll probably want to disable layering checks for the build steps of the transitively used modules. Any thoughts on this?

http://llvm-reviews.chandlerc.com/D2374