RFR: 8134540: Much nearly duplicated code for PerfMemory support [v2]

[Harold Seigel]

> Please review this change to merge the Unix-like PerfMemory_*.cpp source files into a single PerfMemory_posix.cpp source file.
> 
> The changes were tested on Mach5 tiers 1-5 on Linux, Windows, and Mac OS, and cross-builds were done for the S390, arm32, ppc, and x86 platforms.
> 
> Thanks, Harold

Harold Seigel has updated the pull request incrementally with one additional commit since the last revision:

  8134540: changes for review comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2037/files
  - new: https://git.openjdk.java.net/jdk/pull/2037/files/3d6be3bb..db0d9c58

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2037&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2037&range=00-01

  Stats: 113 lines in 3 files changed: 40 ins; 63 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2037.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2037/head:pull/2037

PR: https://git.openjdk.java.net/jdk/pull/2037