test_jit.rb: explicitly skip for unsupported ones

MSP-Greg watches this metrics and this would be helpful for him.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62380 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_jit.rb

@@ -35,14 +35,18 @@ module TestJITSupport
   end
 end
 
-return unless TestJITSupport.supported?
-
 # Test for --jit option
 class TestJIT < Test::Unit::TestCase
   include TestJITSupport
   # Ensure all supported insns can be compiled. Only basic tests are included.
   # TODO: ensure --dump=insns includes the expected insn
 
+  def setup
+    unless TestJITSupport.supported?
+      skip 'JIT seems not supported on this platform'
+    end
+  end
+
   def test_compile_insn_nop
     assert_compile_once('nil rescue true', result_inspect: 'nil')
   end