RFR: JDK-8246751 Mac OS build settings should use -O3

[Magnus Ihse Bursie]

 From Jim's bug report:

"Mac OS X should use -O3 optimization level to be consistent with other 
platforms and benefit Mac OS X java with the same performance levels as 
other platforms.

Mac OS X has used -Os level optimization since management of the 
platform JDK was handed over from Apple. This level of optimization was 
Apple's policy, not OpenJDK's. The policy was established in a time when 
memory was tight (I was there at the time.) Since then other platforms 
have moved on, making the decision to target speed over disk space. 
Specifically, using -O3 level optimization.

I've personally seen 20-30% improvement in performance in C/C++ 
applications using -O3 over -Os. But, of course, the performance team 
should verify the affect on the JDK.

A 11% real time improvement can be seen with a rough HelloWord compile/run."

I discussed this with Claes, our performance guru, and he agreed that it 
is low risk enough that we can push this for JDK 15.

Bug: https://bugs.openjdk.java.net/browse/JDK-8246751
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8246751-macos-optimize-O3/webrev.01

/Magnus