Mark internal utmp functions with attribute_hidden [BZ #18822]

Mark internal utmp functions with attribute_hidden [BZ #18822]

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

	[BZ #18822]
	* include/utmp.h (__updwtmp): Add libc_hidden_proto.
	(__getutent): Likewise.
	(__getutid): Likewise.
	(__getutline): Likewise.
	(__pututline): Likewise.
	(__getutent_r): Likewise.
	(__getutid_r): Likewise.
	(__getutline_r): Likewise.
	(__utmpname): Add attribute_hidden.
	(__setutent): Likewise.
	(__endutent): Likewise.
	* login/getutent.c (__getutent): Add libc_hidden_def.
	* login/getutent_r.c (__getutent_r): Likewise.
	(__pututline): Likewise.
	* login/getutid.c (__getutid): Likewise.
	* login/getutid_r.c (__getutid_r): Likewise.
	* login/getutline.c (__getutline): Likewise.
	* login/getutline_r.c (__getutline_r): Likewise.
	* login/updwtmp.c (__updwtmp): Likewise.