Even better: I have tried to simply replace ld.exe in mingw with clang's (9.0.0) lld.exe and everything works!

Here are times:

with original ld.exe

C:\upp\out\examples\MINGWx64.Debug.Debug_Full.Gui\AddressBoo k.exe (39524957 B) linked in (0:19.68)


with lld.exe

C:\upp\out\examples\MINGWx64.Debug.Debug_Full.Gui\AddressBoo k.exe (36620800 B) linked in (0:00.27)

Thank you Novo for pointing me in the right direction. This is really significant step ahead!