RFR 8235262: Move c2i_entry_barrier for x86_32 to shared

[Roman Kennke]

It looks good to me, thanks!

Roman


> When integrating JDK-8230765 [1], I did not integrate c2i_entry_barrier.
> The implementation is not GC specific, should be moved to shared.
> 
> Again, the implementation is very similar to x86_64 version, except it
> manufactures two temporary registers to act as scratch1 and scratch2
> registers in x86_64.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8235262
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8235262/webrev.00/index.html
> 
> 
> Test:
>   hotspot_gc (fastdebug and release) with x86_64 and x86_32 JVM on Linux
>   submit tests
> 
> 
> Thanks,
> 
> -Zhengyu
> 
> [1] https://bugs.openjdk.java.net/browse/JDK-8230765
>