RFR 8235262: Move c2i_entry_barrier for x86_32 to shared

[Zhengyu Gu]

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