RFR (S) 8217843: Performance regression related to os::supports_monotonic_clock() on linux

[David Holmes]

Bug: https://bugs.openjdk.java.net/browse/JDK-8217843
webrev: http://cr.openjdk.java.net/~dholmes/8217843/webrev/

A simple refactoring to restore some inline function definitions.

Testing: mach5 1-3
Performance testing by Claes - see bug report.

Thanks,
David