I declared all variables in this file so that win32.mak/win64.mak and posix.mak could import only this file.
But while testing it turned out that the digitalmars make include, i.e. `$(.\path\to\file)`, only expands files until the first non-escaped line break so one cannot declare multiple variables in one file.
I'll reintegrate that part into the toplevel posix.mak.