runtime: in sigprof, skip to sigtrampgo if we don't find sigtramp

Fixes https://gcc.gnu.org/PR88202

Change-Id: Ie90b9fe92f565ee677bef2b811e88010ec1920ee
Reviewed-on: https://go-review.googlesource.com/c/158218
Reviewed-by: Cherry Zhang <cherryyz@google.com>