Sync libiberty with GCC.

Sync libiberty with GCC.

libiberty/ChangeLog:
	* d-demangle.c (dlang_call_convention): Handle extern Objective-C
	function calling convention.
	(dlang_call_convention_p): Likewise.
	(dlang_type): Likewise.
	* testsuite/d-demangle-expected: Add coverage tests.

	* d-demangle.c (dlang_function_args): Append ',' for variadic functions
	only if parameters were seen before the elipsis symbol.
	* testsuite/d-demangle-expected: Add coverage test for parameter-less
	variadic functions.

	* d-demangle.c (dlang_type): Handle function types only in the context
	of seeing a pointer type symbol.
	* testsuite/d-demangle-expected: Update function pointer tests.