GCC always recognizes the -fsplit-stack option, but then tests whether
it is supported by the selected target. If not, it reports
    cc1: error: ‘-fsplit-stack’ is not supported by this compiler configuration
Check for that error message when deciding whether a compiler option works.

Change-Id: I2eef8d550bbecba3a087869df2c7351280c77290
Reviewed-on: https://go-review.googlesource.com/87136
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Austin Clements <austin@google.com>