https://bugs.winehq.org/show_bug.cgi?id=45064
--- Comment #2 from Olivier F. R. Dierick o.dierick@piezo-forte.be --- (In reply to Vincent Povirk from comment #1)
Since you are building from a branch, I recommend using the monolite folder from a source tarball.
I copied the ./monolite folder from wine-mono-4.7.1.tar.gz over to the wine-mono GIT tree at the same level as in the tarball and the same error occurred.
The monolite folder contains mcs.exe and a bunch of *.dll.
How do I use it?