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>

libroot/riscv64: Add missing sigjmp's.

Change-Id: Id353f86571ddf5bc106af7c77f0bd3d22b5b7cbd
Reviewed-on: https://review.haiku-os.org/c/1381
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

riscv64: Fill in more bulk architecture items around libroot/kernel

Change-Id: Ia2a86d8814d06950ea2d2d19d966c642d26f81d6
Reviewed-on: https://review.haiku-os.org/c/1302
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>