Fix Math.round in runtime.cc and x64 optimized code.

test/mjsunit/mjsunit.status

 # Copyright 2008 the V8 project authors. All rights reserved.
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 # modification, are permitted provided that the following conditions are
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 #
 #     * Redistributions of source code must retain the above copyright
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@@ skipping 43 matching lines @@
 regress/regress-524: (PASS || TIMEOUT), SKIP if $mode == debug
 
 # Stack manipulations in LiveEdit are buggy - see bug 915
 debug-liveedit-check-stack: SKIP
 debug-liveedit-patch-positions-replace: SKIP
 
 
 ##############################################################################
 [ $arch == arm ]
 
+# Code is bugged. Remove this when fixed.
+math-round: FAIL
+
 # Slow tests which times out in debug mode.
 try: PASS, SKIP if $mode == debug
 debug-scripts-request: PASS, SKIP if $mode == debug
 array-constructor: PASS, SKIP if $mode == debug
 
 # Flaky test that can hit compilation-time stack overflow in debug mode.
 unicode-test: PASS, (PASS || FAIL) if $mode == debug
 
 # Times out often in release mode on ARM.
 compiler/regress-stacktrace-methods: PASS, PASS || TIMEOUT if $mode == release
@@ skipping 34 matching lines @@
 # Requires bigger stack size in the Genesis and if stack size is increased,
 # the test requires too much time to run.  However, the problem test covers
 # should be platform-independent.
 regress/regress-1132: SKIP
 
 ##############################################################################
 [ $arch == mips ]
 
 # Skip all tests on MIPS.
 *: SKIP