gcc, glibc, binutils: Complete missing configuration for building tools for RV32.
gcc: Fix 64 bit multiply on RV32.

Use define_expand instead of define_insn_and_split for 64-bit
multiply on RV32.  With define_insn_and_split, gcc would occasionally
overwrite a source register in the first instruction of a mulhu/mul
pair.
Makefile.in: Allow specification of XLEN when building tools.

This allows building tools for RV64 (default) or RV32.
Merge pull request #10 from darius-bluespec/rv32

Support for building RV32 tools