[x87] Enable test cases which failed at know issue that x87 change sNaN to qNaN by default.

  Since the workaround (CL 36697 : 22a73e0d) for sNaN issue works, enable those test cases.

BUG=

Review-Url: https://codereview.chromium.org/2114853002
Cr-Commit-Position: refs/heads/master@{#37472}

test/mjsunit/mjsunit.status

@@ -648,13 +648,7 @@
 }],  # 'arch == mips'
 
 ##############################################################################
-['arch == x87', {
-  # Turbofan will hit the known issue that x87 changes sNaN to qNaN by default.
-  'regress/regress-undefined-nan': [SKIP],
-  'regress/regress-crbug-242924': [SKIP],
-}],  # 'arch == x87'
 
-##############################################################################
 ['arch == mips64el or arch == mips64', {
 
   # Slow tests which times out in debug mode.