don't ICE when section attribute is used on things in comdats

gcc/

	PR ipa/63621
	* symtab.c (symtab_node::verify): Check for section attribute before
	asserting something isn't in a section and a comdat group.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@218476 138bc75d-0d04-0410-961f-82ee72b054a4