Mark internal statfs functions with attribute_hidden [BZ #18822]

Mark internal statfs functions with attribute_hidden [BZ #18822]

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

	[BZ #18822]
	* include/sys/statfs.h (__fstatfs): Add attribute_hidden.
	(__statfs64): Likewise.
	(__fstatfs64): Likewise.
	* include/sys/statvfs.h (__statvfs64): Likewise.
	(__fstatvfs64): Likewise.
	* sysdeps/unix/sysv/linux/pathconf.h (__statfs_link_max): Likewise.
	(__statfs_filesize_max): Likewise.
	(__statfs_symlinks): Likewise.
	(__statfs_chown_restricted): Likewise.