common: "test-all" depends on "exts" target

This allows me to test changes to ext/ more easily by only typing:

  make test-all TESTS=/path/to/ext/test_foo.rb

I spent a few minutes wondering what was wrong before I realized
changes to exts were not taking effect.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58919 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

common.mk

@@ -676,7 +676,7 @@ test: btest-ruby test-knownbug test-basic
 # $ make test-all TESTOPTS="--help" displays more detail
 # for example, make test-all TESTOPTS="-j2 -v -n test-name -- test-file-name"
 test-all: $(TEST_RUNNABLE)-test-all
-yes-test-all: programs PHONY
+yes-test-all: programs exts PHONY
 	$(gnumake_recursive)$(Q)$(exec) $(RUNRUBY) "$(srcdir)/test/runner.rb" --ruby="$(RUNRUBY)" $(TEST_EXCLUDES) $(TESTOPTS) $(TESTS)
 TESTS_BUILD = mkmf
 no-test-all: PHONY