analyzer testsuite: add explode-2a.c [PR101068]

Due to a bug (PR analyzer/101068), the analyzer only explores a limited
subset of the possible paths through gcc.dg/analyzer/explode-2.c,
and this artifically helps stop this testcase from exploding.
I intend to fix this at some point, but for now, this patch adds a
revised test case which captures the effective CFG due to the bug, so
that we explicitly have test coverage for that CFG.

gcc/testsuite/ChangeLog:
	PR analyzer/101068
	* gcc.dg/analyzer/explode-2a.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>