RFR: 8067306: Improve STATIC_ASSERT

[Kim Barrett]

Please review this enhancement to the hotspot STATIC_ASSERT() macro.

I will also need a sponsor for this change.

[Note: Although this is in "runtime", development was done in hs-gc
rather than hs-rt, and I'd rather have it pushed via hs-gc. The point
of making this change was that I wanted it for some other work I'm
doing. I'd rather not wait for repo reconcilliation, and I don't think
anyone else is champing at the bit for this.]

CR:
https://bugs.openjdk.java.net/browse/JDK-8067306

Webrev:
http://cr.openjdk.java.net/~kbarrett/8067306/webrev/

Testing:

JPRT with temporary static assertions inserted at top-level, at class
scope, and with value dependent on a template parameter, to verify the
macro can now be used in those contexts. [The code base already
contains several uses in function bodies, including with template
dependencies.]

JPRT with temporary intentional static assertion failures at
top-level, class scope, function scope, and with value dependent on a
template parameter, to verify expected failures occurred, and that the
compiler error messages were informative.