RFR (11): Revert to emit locked cmpxchg only on MP

[Roman Kennke]

>> Last backports introduced a minor diff vs. upstream that we can and
>> should revert:
>>
>> http://cr.openjdk.java.net/~rkennke/jdk11-revert-lock-cas/webrev.00/
> 
> Looks good.
> 
> I think there is a white-space difference here:
>  1942    } else {
> 
> See:
> 
> https://builds.shipilev.net/patch-openjdk-shenandoah-jdk11/src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp.sdiff.html
> 
> Can you "hg diff -r 435ba0b576c9 src/hotspot/cpu/x86/c1_LIRAssembler_x86.cpp" to see it?

I'll revert that WS diff too, ok?

Roman