build: avoid gcc preprocessor extensions

build: avoid gcc preprocessor extensions

Use of ',##__VA_ARGS__' is a gcc extension not guaranteed by
C99; thankfully, we can avoid it by lumping the format argument
into the var-args set.

* src/util/logging.h (VIR_DEBUG_INT, VIR_INFO_INT, VIR_WARN_INT)
(VIR_ERROR_INT, VIR_DEBUG, VIR_INFO, VIR_WARN, VIR_ERROR): Stick
to C99 var-arg macro syntax.
* examples/domain-events/events-c/event-test.c (VIR_DEBUG):
Simplify.