[-cxx-abi microsoft] Mangle UUIDs correctly, stick them in the proper section

We mangled them like:
L___uuid_12345678-1234-1234-1234-123456789abc

We should've mangled them like:
__GUID_12345678_1234_1234_1234_123456789abc

Furthermore, they are external symbols.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188053 91177308-0d34-0410-b5e6-96231b3b80d8