RFR: 8148844: Update run_unit_test macro for InternalVMTests

[Erik Helin]

Hi all,

this patch updates the run_unit_test macro for InternalVMTests.
The new macro both forward declares the test function and runs it. C++
can (as opposed to C) forward declare a function inside another
function. I also added a small helper function, run_test, that
ensures that test functions must return void and take no parameters (by
typing the test function as a function pointer).

Webrev:
http://cr.openjdk.java.net/~ehelin/8148844/00/

Enhancement:
https://bugs.openjdk.java.net/browse/JDK-8148844

Testing:
- JPRT
- Running the tests locally

Thanks,
Erik