I had a quick go at getting mono/C# built with this. I got the glue built fine and even grabbed msbuild from mono:factory. The sticking point was nuget. Maybe we can use a precompiled version from nuget's website and do

SourceX:nuget.exe

alias nuget="mono nuget.exe"

as per https://docs.microsoft.com/en-us/nuget/install-nuget-client-tools

Second consideration is that msbuild is also a hack job and is a recompile of the centos build.

https://build.opensuse.org/package/show/Mono:Factory/msbuild

I don't think that has a hope in hell of getting into factory but may only be needed for the build. To unravel MS's mess so that it can be securely built is probably too much work if it's a "requires".

If you're building godot with c# support, hopefully the above will give you a good starting place. Effectively the changes were only...

BuildRequires:  pkgconfig(mono)
BuildRequires:  pkgconfig(monosgen-2)
BuildRequires:  msbuild


# Build temp mono glue binary (removed extra build args to prevent seg fault)
scons %{?_smp_mflags} progress=yes verbose=yes $system_libs platform=server tools=yes module_mono_enabled=yes mono_glue=no

# Build mono glue with bin/godot_server.x11.tools.64.mono
./bin/%{name}_server.x11.tools.%{__isa_bits}.mono --generate-mono-glue modules/mono/glue

#then the editors etc with module_mono_enabled=yes appended

that got me as far as the nuget error when the editor was building after this part.