Fix for PECOFF GetArchitecture

0 as CPU subtype never matches anything (at least, it doesn't match x86_64 windows binaries, of which there are correct arch definitions for). It should be created with LLDB_INVALID_CPUTYPE. 

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@195435 91177308-0d34-0410-b5e6-96231b3b80d8