nmethod_entry_barrier stub miscalculates xmm spill size on x86_32

Reproducible with:
$ CONF=linux-x86-server-fastdebug make images run-test TEST=java/lang/invoke/VarHandles/ TEST_VM_OPTS="-XX:+UseShenandoahGC"

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Test summary
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   TEST TOTAL PASS FAIL ERROR
>> jtreg:test/jdk/java/lang/invoke/VarHandles 37 31 6 0 <<
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Most of them fail only with Shenandoah with:

java.lang.AssertionError: success compareAndExchangeRelease float value expected [1.690906E7] but found [0.0]
at org.testng.Assert.fail(Assert.java:94)
at org.testng.Assert.failNotEquals(Assert.java:496)
at org.testng.Assert.assertEquals(Assert.java:125)
at VarHandleTestByteArrayAsFloat.testArrayReadWrite(VarHandleTestByteArrayAsFloat.java:1243)
at VarHandleTestByteArrayAsFloat.lambda$accessTestCaseProvider$11(VarHandleTestByteArrayAsFloat.java:190)
at VarHandleBaseTest$AccessTestCase.testAccess(VarHandleBaseTest.java:405)