We don't need quite so much duplication because we already have a way
to get the signal number from its name, and that already copes with the
fact that the mips/mips64 numbers are different from everyone else's.
Also remove sys_signame from LP64. glibc doesn't have this BSD-ism.
Change-Id: I6dc411a3d73589383c85d3b07d9d648311492a10
