fix visibility mismatch in dynamic linker stage 2 function definition

fix visibility mismatch in dynamic linker stage 2 function definition

since commits 2907afb8dbd4c1d34825c3c9bd2b41564baca210 and
6fc30c2493fcfedec89e45088bea87766a1e3286, __dls2 is no longer called
via symbol lookup, but instead uses relative addressing that needs to
be resolved at link time. on some linker versions, and/or if
-Bsymbolic-functions is not used, the linker may leave behind a
dynamic relocation, which is not suitable for bootstrapping the
dynamic linker, if the reference to __dls2 is marked hidden but the
definition is not actually hidden. correcting the definition to use
hidden visibility fixes the problem.

the static-PIE entry point rcrt1 was likewise affected and is also
fixed by this patch.