runtime: declare runtime_usestackmaps in stack.c, not runtime.h

Fixes https://gcc.gnu.org/PR92605

Change-Id: I4df832cd544ad042ba31d9db69936ed5d280fdb8
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/208161
Reviewed-by: Cherry Zhang <cherryyz@google.com>
2 files changed