RFR(S) 8231986 [SA] Consolidate parts of the Linux and MacOSX versions of ps_core.c

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8231986
http://cr.openjdk.java.net/~iklam/jdk14/8231986-consolidate-ps-core.v01/

One of my upcoming CDS changes (JDK-8231610) would affect the duplicated 
code
in these 2 files. So instead of fixing the same thing twice, I have 
moved the
duplicated parts of these files that are related to CDS into a common file.
This would simplify future maintenance of CDS+SA code.

To make my life simple, I just moved all functions up to 
init_classsharing_workaround().
The remaining lines of the these 2 files seem to be unrelated to hotspot 
(core file
handling, elf, etc), so they probably don't need to be changed any time 
soon. I'll leave
the duplications there as is.

Thanks
- Ioi