Add fast-variants feature to test driver.

test/mjsunit/mjsunit.status

Index: test/mjsunit/mjsunit.status
diff --git a/test/mjsunit/mjsunit.status b/test/mjsunit/mjsunit.status
index 6b3cf844ca251b9cc68e615bae86a5a476131ecd..723f0e8c8de4e89e16f3dda89ea292cd30c9609b 100644
--- a/test/mjsunit/mjsunit.status
+++ b/test/mjsunit/mjsunit.status
@@ -31,11 +31,6 @@
   'bugs/*': [FAIL],
 
   ##############################################################################
-  # Slow tests.
-  'asm/embenchen/box2d': [PASS, SLOW],
-  'asm/embenchen/lua_binarytrees': [PASS, SLOW],
-
-  ##############################################################################
   # Flaky tests.
   # BUG(v8:2921).
   'debug-step-4-in-frame': [PASS, FAIL, SLOW],
@@ -205,6 +200,9 @@
 
   # This test variant makes only sense on arm.
   'math-floor-of-div-nosudiv': [PASS, SLOW, ['arch not in [arm, arm64, android_arm, android_arm64]', SKIP]],
+
+  # Too slow for slow variants.
+  'asm/embenchen/*': [PASS, FAST_VARIANTS]
 }],  # ALWAYS
 
 ##############################################################################