[dev] Add 'all' targets back to Makefiles.

Change-Id: I4dcf2ed1c9edf713bdf20cdb844599921e36566c

protoc-gen-go/Makefile

@@ -29,6 +29,8 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+all: test
+
 test:
 	go test
 	cd testdata && make test

protoc-gen-go/testdata/Makefile

@@ -29,5 +29,7 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+all: test
+
 test:
 	go test