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Ready for review

While you're working on this area of dmd it might be good to sort out dmd's behaviour WRT lib. If I understand the bug correctly it actually overwrites the LIB environment variable rather than appending to it.

I think so. Appending the correct path to LIB would enable the linker to find the correct libraries but still fail because dmd then passes MsCoff files to OPTLINK (configured by LINKCMD)