libgo: pass $(NM) value when running benchmarks

On AIX, we need to use "nm -B" instead of "nm", to have the
epxected output format, so the configured $(NM) value from
the Makefile should be exported before running gotest, which
defaults to "nm" if $NM is not set.

Issue golang/go#19200

Change-Id: If2550d60d0955e664d394c6b90c1afe2b1b8af8d
Reviewed-on: https://go-review.googlesource.com/42051
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed