After installation, on a Win7 64 bit system, rustc fails immediately with:
The program can't start because libgcc_s_dw2-1.dll is missing from your computer. Try reinstalling the program to fix this problem.
dependency walker thinks its a direct requirement of RUSTRT.DLL and RUSTLLVM.DLL, The other dependencies suggest that these were build with mingw, I suspect - why not with clang or msdev?
IESHIMS.DLL is also missing on my system, but its delay-load.
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Anyway - I think you need to ship mingw runtime components. And that probably means license pain too, even if its just to reference the licenses and indicate where to get the sources.