gcc: Add soft-float conversion stubs to riscv-elf.

Add missing software floating point conversion stubs to libgcc for riscv-elf
(non-Linux).
Merge pull request #6 from darius-bluespec/softfloat

gcc: Add soft-float conversion stubs to riscv-elf.
Support [dis]assembling 48/64-bit insns
Set glibc minimum ABI to 2.14

We don't need backwards compatibility, and this reduces code size.