cmd/internal/obj/riscv: mark stack bounds check prologue nonpreemptible

This is similar to CL 207350, for RISCV64.

May fix #50263.
Updates #35470.

Change-Id: I0d39e195e8254d65fa1aca1cdf1fc553aa8b7cba
Reviewed-on: https://go-review.googlesource.com/c/go/+/373434


Trust: Cherry Mui <cherryyz@google.com>
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Reviewed-by: David Chase <drchase@google.com>
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