module 'conflict' stanza doesn't work across top-level modules

[Quuxplusone]

Bugzilla Link	PR19358
Status	NEW
Importance	P normal
Reported by	Richard Smith (richard-llvm@metafoo.co.uk)
Reported on	2014-04-07 12:22:24 -0700
Last modified on	2014-10-03 21:18:13 -0700
Version	unspecified
Hardware	PC All
CC	dgregor@apple.com, llvm-bugs@lists.llvm.org
Fixed by commit(s)
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Repro:

module A {}
module B { conflict A }

Building B will assert, because it tries to allocate a submodule ID for 'A',
which is neither part of the currently-building module nor in a module that it
imports.

[Quuxplusone]

We get a similar failure if a module exports another top-level module that it
doesn't otherwise depend on. Here's a lit test:

// RUN: rm -rf %t
// RUN: %clang_cc1 -fmodules -emit-module -fmodule-name=B -x c++ %s -fmodules-
cache-path=%t
// RUN: %clang_cc1 -fmodules -emit-module -fmodule-name=A -x c++ %s -fmodules-
cache-path=%t
// RUN: %clang_cc1 -fmodules -emit-module -fmodule-name=C -x c++ %s -fmodules-
cache-path=%t
module A {}
module B { conflict A, "can't have A and B together" }
module C {
  export A
  export B
}