libgo: don't use wc in gotest

    
    The wc command is not in the GNU approved list of Makefile utilities
    (https://www.gnu.org/prep/standards/html_node/Utilities-in-Makefiles.html#Utilities-in-Makefiles).
    
    Reviewed-on: https://go-review.googlesource.com/c/144897

From-SVN: r265515