In 'gcc/omp-oacc-kernels-decompose.cc:flatten_binds', don't choke on empty GIMPLE...

In 'gcc/omp-oacc-kernels-decompose.cc:flatten_binds', don't choke on empty GIMPLE sequence

Also, instead of just examining the first statement of inner 'GIMPLE_BIND' (via
'inner_sequence' being a 'typedef gimple *gimple_seq'), in fact examine all
statements contained therein, which I suppose must've been the intention here.

This "fixes" the testcase 'c-c++-common/goacc/kernels-decompose-ice-2.c' (which
now runs into the same ICE as 'c-c++-common/goacc/kernels-decompose-ice-1.c',
etc.).

	gcc/
	* omp-oacc-kernels-decompose.cc (flatten_binds): Don't choke on
	empty GIMPLE sequence, and examine all statements contained in
	inner 'GIMPLE_BIND'.
	gcc/testsuite/
	* c-c++-common/goacc/kernels-decompose-ice-1.c: Adjust.
	* c-c++-common/goacc/kernels-decompose-ice-2.c: Likewise.