Are there any working instructions about how to build and test dmd on Windows?

[Rubn]

Yah it's not fun.

Some notes:

You might need to set MSVC_CC environment variable cause it 
doesn't use the right format for VS path, depending on your 
version.

https://github.com/dlang/dmd/blob/v2.079.0/src/vcbuild/msvc-dmc.d#L19


You could open a command prompt with the batch file running which 
will add variables used by the script.

C:/Program Files (x86)/Microsoft Visual Studio 
14.0/VC/vcvarsall.bat


You should be able to build it now with just:

make -f win64.mak reldmd


When building druntime/phobos you need to pass the VCINSTALLDIR 
environment variable, but it has an unexpected "/" at the end of 
it so you need to remove it.

make -f win64.mak VCDIR="%VCINSTALLDIR:~0,-1%" DMD=../dmd/src/dmd

Didn't check if it works though I don't normally use batch/cmd.