Module: Do not add any link flags when an implementation TU of a module imports
a header of that same module.

This fixes a regression caused by r280409.
rdar://problem/29930553

This is an updated version for r291628 (which was reverted in r291688).

llvm-svn: 291689
diff --git a/clang/test/Modules/Inputs/module-impl-with-link/foo.h b/clang/test/Modules/Inputs/module-impl-with-link/foo.h
new file mode 100644
index 0000000..90fe1bc
--- /dev/null
+++ b/clang/test/Modules/Inputs/module-impl-with-link/foo.h
@@ -0,0 +1 @@
+//empty