Bug 33963

Testcase gcc.dg/attr-invalid.c started failing on mingw32 with

http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=125975

In particular, this delta
	* tree.c (handle_dll_attribute): Set DECL_VISIBILITY on the
	imported or exported declaration, including type declarations.
 
made these TYPE_DECL's valid:

# 88 "attr-invalid.c"
typedef int dllimport_type __attribute__((dllimport));

typedef int (*dllimport_fntype)(void) __attribute__((dllimport));

Prior to that revision the attribute was valid only on FUNCTION_DECLS's
and VAR_DECL's 

However, although there is no warning, the attribute is ignored 

typedef int dllimport_type __attribute__((dllimport));
extern dllimport_type foo;
int bar () { return foo; }

gives

_bar:
	pushl	%ebp
	movl	%esp, %ebp
	movl	_foo, %eax
	popl	%ebp
	ret