Hide internal printf functions [BZ #18822/21986]

Hide internal printf functions to allow direct access within libc.so and
libc.a without using GOT nor PLT.

Since __guess_grouping has been changed to take 2 arguments by

commit a1d84548
Author: Ulrich Drepper <drepper@redhat.com>
Date:   Fri Feb 11 18:50:36 2000 +0000

the third argument passed to __guess_grouping is removed.

	[BZ #18822]
	[BZ #21986]
	* include/printf.h (__printf_fphex): Add attribute_hidden.
	(__guess_grouping): New prototype.
	* stdio-common/printf_fp.c (__guess_grouping): Removed.
	* stdio-common/reg-printf.c (__register_printf_specifier): Add
	libc_hidden_proto and libc_hidden_def.
	* stdlib/strfmon_l.c (__guess_grouping): Removed.
	(__vstrfmon_l): Remove the third argument passed to
	__guess_grouping.