PR c/28299
	* c-decl.c (start_function): Don't try to process prototype
	information from old declaration that isn't a function.

testsuite:
	* gcc.dg/funcdef-var-1.c, gcc.dg/funcdef-var-2.c: New tests.
	* gcc.dg/pr20368-1.c, gcc.dg/pr20368-2.c, gcc.dg/pr20368-3.c:
	Expect extra diagnostics.

From-SVN: r116435