target/riscv/kvm: do not use non-portable strerrorname_np()

target/riscv/kvm: do not use non-portable strerrorname_np()

strerrorname_np is non-portable and breaks building with musl libc.

Use strerror(errno) instead, like we do other places.

Cc: qemu-stable@nongnu.org
Fixes: commit 082e9e4a58ba (target/riscv/kvm: improve 'init_multiext_cfg' error msg)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2041
Buglink: https://gitlab.alpinelinux.org/alpine/aports/-/issues/15541
Signed-off-by: Natanael Copa <ncopa@alpinelinux.org>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit d424db235434b8356c6b2d9420b846c7ddcc83ea)