Disable "-Werror" during binutils builds

Some shared binutils source code throws some harmless looking errors
with newer GCC versions.  This patch stops failing the binutils build
whenever these errors show up.

Both Gentoo and LFS set this flag, so I think it's sane.
glibc: make fe{get|set}round globally visible
gcc: build riscv64-unknown-linux-gnu-gfortran
gcc: remove broken peephole optimizers

These weren't really helping, and the FP ones were causing occasional ICEs.