Prevent lookup of subframework modules by name without parent framework

We were 'allowing' the following import
@import Sub;

where Sub is a subframework of Foo and we had a -F path inside
Foo.framework/Frameworks and no module map file for Sub. This would
later hit assertion failures in debug builds.

Now we should correctly diagnose this as a module not found error.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204368 91177308-0d34-0410-b5e6-96231b3b80d8
Coding style fixup; no functionality change

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204371 91177308-0d34-0410-b5e6-96231b3b80d8
Use nullptr; no functionality change

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204372 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Fix a bad bug in reversePropagateInterstingSymbols() where only one subexpression of BinaryOperator would be explored.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204374 91177308-0d34-0410-b5e6-96231b3b80d8
Remove dead assignment dominated by a call to llvm_unreachable().

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204375 91177308-0d34-0410-b5e6-96231b3b80d8
[-Wunreachable-code] Tweak isTrivialDoWhile() to handle implicit casts.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204376 91177308-0d34-0410-b5e6-96231b3b80d8