libgo: add -L option for libatomic when using -pthread

Fixes https://gcc.gnu.org/PR84484

Change-Id: I42c9909539ee1a08cd79710ddddc1700571ebae6
Reviewed-on: https://go-review.googlesource.com/95436
Reviewed-by: Than McIntosh <thanm@google.com>
2 files changed