Propagate type attribute when merging extern declarations at local scope.

Propagate type attribute when merging extern declarations at local scope.

Resolves:
PR c/99420 - bogus -Warray-parameter on a function redeclaration in function scope
PR c/99972 - missing -Wunused-result on a call to a locally redeclared warn_unused_result function

gcc/c/ChangeLog:

	PR c/99420
	PR c/99972
	* c-decl.c (pushdecl): Always propagate type attribute.

gcc/testsuite/ChangeLog:

	PR c/99420
	PR c/99972
	* gcc.dg/Warray-parameter-9.c: New test.
	* gcc.dg/Wnonnull-6.c: New test.
	* gcc.dg/Wreturn-type3.c: New test.
	* gcc.dg/Wunused-result.c: New test.
	* gcc.dg/attr-noreturn.c: New test.
	* gcc.dg/attr-returns-nonnull.c: New test.