testsuite/gdb.base: Make skip test use defined behaviour.

testsuite/gdb.base: Make skip test use defined behaviour.

The skip test currently relies on the order of evaluation of
arguments which is not defined. Use the comma operator where
order is defined instead.

gdb/testsuite/ChangeLog:

2013-06-18  Will Newton  <will.newton@linaro.org>

	* gdb.base/skip.c: Use comma to evaluate results of foo()
	and bar() before passing to baz().
	* gdb.base/skip.c: baz() now takes one argument instead of
	two.