Link libraries depended on by LLVM

This explicitly pulls in higher-order library dependencies, and gets us closer to building on windows. Unfortunately, on my configuration I still have undefined references to `_imp__SymSetOptions@4` and `_imp__SymInitialize@12` (note single leading underscores). SymSetOptions and SymInitialize are ostensibly provided by libdbghelp.a, but nm only detects versions with two leading underscores there.