Mark internal stdio functions with attribute_hidden [BZ #18822]

Mark internal stdio functions with attribute_hidden [BZ #18822]

Mark internal stdio functions with attribute_hidden to allow direct
access within libc.so and libc.a without using GOT nor PLT.

	[BZ #18822]
	* include/stdio.h (__fcloseall): Add attribute_hidden.
	(__getline): Likewise.
	(__path_search): Likewise.
	(__gen_tempname): Likewise.
	(__libc_message): Likewise.
	(__flockfile): Likewise.
	(__funlockfile): Likewise.
	(__fxprintf): Likewise.
	(__fxprintf_nocancel): Likewise.