RFR (S) 8241583: Shenandoah: turn heap lock asserts into macros

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8241583

See rationale in the bug.

Webrev:
  https://cr.openjdk.java.net/~shade/8241583/webrev.01/

Testing: hotspot_gc_shenandoah {fastdebug, release}

-- 
Thanks,
-Aleksey