fix garbage benchmark Makefile.

apparently some versions of GNU make cannot
handle the %: %.$O rule.  i don't understand why
and don't care enough to find out.

R=agl1
CC=golang-dev
https://golang.org/cl/206055

.hgignore

@@ -32,9 +32,7 @@ src/pkg/runtime/runtime.acid.*
 test/pass.out
 test/run.out
 test/times.out
-test/garbage/parser
-test/garbage/peano
-test/garbage/tree
+test/garbage/*.out
 
 syntax:regexp
 ^pkg/

test/garbage/Makefile

@@ -9,16 +9,16 @@ ALL=\
 	peano\
 	tree\
 
-all: $(ALL)
+all: $(addsuffix .out, $(ALL))
 
 %.$O: %.go
 	$(GC) $*.go
 
-%: %.$O
+%.out: %.$O
 	$(LD) -o $@ $*.$O
 
-%.bench: %
-	./$*
+%.bench: %.out
+	./$*.out
 
 bench: $(addsuffix .bench, $(ALL))