RFR: [backport] 8202976: Add C1 lea patching support for x86

[Roman Kennke]

This backports this change:

https://bugs.openjdk.java.net/browse/JDK-8202976

to shenandoah/jdk8

This is prerequisite for SFX barriers which I will post next. It is not 
Shenandoah-specific per-se, but only required for Shenandoah atm. I 
don't think it makes sense to bother upstream with it.

The change itself is a straightforward backport from jdk11:

http://cr.openjdk.java.net/~rkennke/JDK-8202976-jdk8/webrev.00/

Testing: hotspot_gc_shenandoah (also with upcoming SFX change, which 
actually uses it)

Ok?

Thanks,
Roman