Fix redefinition of default argument, found by modules build.  It's not
entirely clear whether this should be valid with modules enabled, but the fixed
code is cleaner regardless.

Also fix a TU-local type that accidentally had external linkage.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206714 91177308-0d34-0410-b5e6-96231b3b80d8