Make sure that Module::ConfigMacrosExhaustive gets initialized and deserialized correctly.

This fixes regressions introduced in r177466 that caused several
module tests to fail sporadically.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177481 91177308-0d34-0410-b5e6-96231b3b80d8