libgo: pass flags to recursive make

"make check" runs make recursively to check each package. Pass
the flags through. So it is possible to run "make check" with
different settings easily.

Change-Id: If76f2712f5a47178629e65638b73157d2a02a780
Reviewed-on: https://go-review.googlesource.com/76029
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
2 files changed