Mark internal stdlib functions with attribute_hidden [BZ #18822]

Mark internal stdlib functions with attribute_hidden [BZ #18822]

Mark internal stdlib functions with attribute_hidden to allow direct
access within libc.so and libc.a without using GOT nor PLT.  __realpath
is hidden with libc_hidden_proto and libc_hidden_def since the exported
realpath is an alias of __realpath.

	[BZ #18822]
	* include/stdlib.h (__random): Add attribute_hidden.
	(__random_r): Likewise.
	(__srandom_r): Likewise.
	(__initstate_r): Likewise.
	(__setstate_r): Likewise.
	(__erand48_r): Likewise.
	(__nrand48_r): Likewise.
	(__jrand48_r): Likewise.
	(__srand48_r): Likewise.
	(__seed48_r): Likewise.
	(__lcong48_r): Likewise.
	(__drand48_iterate): Likewise.
	(__setenv): Likewise.
	(__unsetenv): Likewise.
	(__clearenv): Likewise.
	(__ptsname_r): Likewise.
	(__posix_openpt): Likewise.
	(__add_to_environ): Likewise.
	(__realpath): Add libc_hidden_proto.
	(__ecvt_r): Likewise.
	(__fcvt_r): Likewise.
	(__qecvt_r): Likewise.
	(__qfcvt_r): Likewise.
	* misc/efgcvt_r.c (cvt_symbol_1): Add libc_hidden_def (local).
	* stdlib/canonicalize.c (__realpath): Add libc_hidden_def.