glibc: Hack and slash in riscv64

* This isn't perfect, but should be a solid start.

Change-Id: Icb3f8c57b2bc4148d2ac14a71375d3f36c15e13b
Reviewed-on: https://review.haiku-os.org/c/1403
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>