numrun012(ghci) now passes on Windows

I don't know why it started working, but we didn't know why it didn't work
before either.
Handles TEST_HC=c:/... on Windows
Fix T7037 on Windows
Tweak a comment to help vim's syntax highlighting
dynCompileExpr(dyn) fails on Windows as ghc isn't built the dyn way
Make T7037 work on both Windows and other platforms