TestCPUProfileLabel was failing on windows/arm because the link register
was not being passed to sigprof(). The link register is required to
generate a correct traceback. With this change, all tests in runtime.pprof
are now passing.

Updates #26148

Change-Id: Ia693b34278dc08a98023751ff1a922d9eee8fdd6
Reviewed-on: https://go-review.googlesource.com/c/153839
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>