RFR(s): 8218145: block_if_requested is not proper inlined due to size

[Robbin Ehn]

Hi all, please review.

Code:
http://cr.openjdk.java.net/~rehn/8218145/webrev/index.html
Issue:
https://bugs.openjdk.java.net/browse/JDK-8218145

SafepointMechanism::block_if_requested(JavaThread*) is often not inlined to due 
inline-unit-growth.
This improve the inlining frequency with 6-7x.
Some startup benchmarks show 1% better time.

Test -+ThreadsLocalHandshakes and t1.

Note that we are planning to deprecate -ThreadsLocalHandshakes in 13, therefore 
-ThreadsLocalHandshakes is put in slow path to further reduce size.
When we can remove the uses_thread_local_poll() it become so small it is always 
inlined. Arguably this method should have ALWAYSINLINE, but I would prefer not.

Thanks, Robbin