compiler: intrinsify sync/atomic functions

Let the Go frontend recognize sync/atomic functions and turn them
into intrinsics.

Also make sure not to intrinsify calls in go or defer statements.

Change-Id: I0b2ead31cb4f44f3ed739416643675f80af72a51
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/178937
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed