I tried 'make all-stage1 STAGE1_LANGUAGES=c++,fortran'. Not only that didn't work, it wiped the directory <bld>/gcc/testsuite.
I believe it was only relocated in stage3-gcc/testsuite.Right now to change the STAGE1_LANGUAGES, you have to remove the stage1-gcc directory. I have a patch to fix this; I'm not sure that the slush is the best time to submit it though.
Paolo