Do not use RW mutexes on RISC-V arch

Do not use RW mutexes on RISC-V arch

For unknown reasons using RW mutexes on RISC-V arch
seems to be broken, at least with glibc.

Fixes #28550

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28635)

(cherry picked from commit 728d5cf9e1b1bed196b31e8c71b8e1d2e398d2ff)