[MinGW] Always emit local typeinfo

This makes sure that code built with headers for a statically linked
libc++ also works when linking to the DLL version, when the DLL
hasn't been built with --export-all-symbols.

This matches what GCC for MinGW does for this test case.

Differential Revision: https://reviews.llvm.org/D61177

llvm-svn: 359345