[runtime] [test] Use more portable short options to sort(1)

Pass `-n -s` instead of `--numeric --stable` to sort(1), as long options
are not supported by NetBSD sort implementation.  `-n` is defined
by POSIX, so it should be fully portable.  `-s` is used consistently
at least in GNU sort and FreeBSD sort, and I honestly doubt it would
cause issues with any other implementation supporting `--stable`.

Differential Revision: https://reviews.llvm.org/D55479

llvm-svn: 348855