Re: gas: add visibility support using GNU syntax on XCOFF

tc-ppc.c: In function 'ppc_comm':
tc-ppc.c:4560:40: error: 'visibility' may be used uninitialized in this function [-Werror=maybe-uninitialized]

With that fixed we hit lots of segfaults in the ld testsuite.

	PR 22085
bfd/
	* xcofflink.c (xcoff_link_input_bfd): Don't segfault on NULL
	sym_hash.
gas/
	* config/tc-ppc.c (ppc_comm): Init visibility.