When we're emitting a diagnostic with a source location in an imported
module, provide a module import stack similar to what we would get for
an include stack, e.g.,

In module 'DependsOnModule' imported from build-fail-notes.m:4:
In module 'Module' imported from DependsOnModule.framework/Headers/DependsOnModule.h:1:
Inputs/Module.framework/Headers/Module.h:15:12: note: previous definition is here
@interface Module

<rdar://problem/12696425>


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@169042 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed