On Windows 11, trying to build with compiler: ghc-git-682bf9799b3c3037ee484732bd83c3d21f620fc0 was failing during Stage 1, with:
_build/stage0/bin/ghc.exe: createProcess: does not exist (No such file or directory)
even though _build/stage0/bin/ghc.exe had been created during Stage 0.
The reason seems to be a problem with long paths (even though long paths support was enabled). Creating, short, C:\Temp and setting TEMP and TMP to reference it saw GHC built from source.
However, the build has folder lib\targets containing file default.target and that file has absolute paths. The built GHC does not work, as a consequence.