The guide is referring A | B NOT A & B.
While the board you are using is custom so modulator also have no obligation to make it able to build.
While I had compile xc7z100 custom board successfully (MANY TIMES).
Using make Prebuilt=XXXX BOARDS=XXXX
Build guide 2.7 & 3.0:
@stf
Could help a bit a better explanation about the TWO make command.