Revert of X87: disable the regress-undefined-nan test case for x87.

test/mjsunit/mjsunit.status

Index: test/mjsunit/mjsunit.status
diff --git a/test/mjsunit/mjsunit.status b/test/mjsunit/mjsunit.status
index e564a912607d31758d2708c480e1e804d0286e0b..595fc6f4c1f8c09c5ad258b93994f8c12132eec6 100644
--- a/test/mjsunit/mjsunit.status
+++ b/test/mjsunit/mjsunit.status
@@ -566,12 +566,6 @@
 }],  # 'arch == mips'
 
 ##############################################################################
-['arch == x87', {
-  # Turbofan will hit the known issue that x87 changes sNaN to qNaN by default.
-  'regress-undefined-nan': [SKIP],
-}],  # 'arch == x87'
-
-##############################################################################
 ['arch == mips64el or arch == mips64', {
 
   # Slow tests which times out in debug mode.