Hi Gravis,
For the 4.7 branch, the documentation that is automatically built has some comments that are now parsed as incorrect by version 5 of makeinfo, so that is why you are seeing that error.
For the 4.8 branches, I am assuming you just ran 'make' after configure. This tries to build some libraries (libgcc, libstdc++) that require the target assembler. As that isn't available the build is failing. If you try 'make all-gcc' and to install 'make install-gcc' instead of just make and make install, that should fix your problem.