RFR: JDK-8273979: move some os time related functions to os_posix for POSIX platforms [v2]

[Matthias Baesken]

> There are a couple of time related functions in os_<platform> for Linux, BSD+Mac and AIX that are pretty similar (or identical) across the platforms and can be centralized in os_posix .
> While doing so, I noticed that  os::supports_vtime()   returns always true , on Posix and also on Windows, so we might remove it completely if this prefered ? 
> 
> Best regards , Matthias

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  Restored javaTimeNanos_info in os-files, adjusted clock_tics_per_sec init

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5582/files
  - new: https://git.openjdk.java.net/jdk/pull/5582/files/fb75bd14..91bd15ae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5582&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5582&range=00-01

  Stats: 25 lines in 3 files changed: 18 ins; 6 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5582.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5582/head:pull/5582

PR: https://git.openjdk.java.net/jdk/pull/5582