The good news, I was able to compile and install Clang and lld from branch llvmorg-12.0.1 under Windows / Cygwin. It compiles my code fine but linker says:
lld: error: unknown argument: --dll-search-prefix=cyg
I am wondering because of I thought lld takes the same cli parameters as ld.
I am working on a project which includes gtest and uses the cmake framework. The files for testing are linked as library and later again the tests and finally again gtest. The code is linking and working when using ggc 11.2.0
--dll-search-prefix is a win32-specific option of ld which is not (yet) implemented in lld.