RFR(XXXS): 7194409: os::javaTimeNanos() shows hot on CPU_CLK_UNHALTED profiles

[John Cuthbertson]

Hi Everyone,

Can I have another volunteer to review the changes for this CR (which 
were contributed by Brandon Mitchell at Twitter)? The webrev can be 
found at: http://cr.openjdk.java.net/~johnc/7194409/webrev.0/

Here's the description, according to Brandon:

> os::javaTimeNanos() shows hot on CPU_CLK_UNHALTED profiles due to
> unnecessary function setup/teardown code around
> Linux::supports_monotonic_clock(). I've added an inline annotation to
> simplify the funcall to a NULL check, and verified the change using
> both gdb disas and additional profiling. I observed a 2-3% CPU time
> delta in my profile data for os::javaTimeNanos().
>   
Thanks,

JohnC