RFR: 8086027: Multiple STATIC_ASSERTs at class scope doesn't work

[Kim Barrett]

Third time's the charm?

Please review this change to the STATIC_ASSERT macro, to allow
multiple assertions in the same class scope.

It seems we do need to make the typedef names used in the expansion
unique per scope; see CR for details.  We accomplish this with
preprocessor token pasting with __LINE__ (done correctly, unlike in
the change for JDK-8067306).

Apparently my testing for JDK-8073994 missed the class scope case.
With this change set I'm adding tests for all three of namespace,
class, and function scope.

As part of this, I'm also adding PASTE_TOKENS(x, y) utility macro.
I'm willing to entertain alternative naming suggestions, though hoping
to avoid a bikeshed discussion.

CR:
https://bugs.openjdk.java.net/browse/JDK-8086027

Webrev:
http://cr.openjdk.java.net/~kbarrett/8086027/webrev.00/

Testing:
JPRT