fix time64 link regression of dlsym stub for static-linked programs

fix time64 link regression of dlsym stub for static-linked programs

in commit 22daaea39f1cc5f7391f0a5cd84576ffb58c2860, the
__dlsym_redir_time64 function providing the backend for __dlsym_time64
was defined only in the dynamic linker, and thus was undefined when
static linking a program referencing dlsym. use the same stub_dlsym
definition that provides __dlsym (the non-redirecting backend) for
static linked programs to provide it, conditional on _REDIR_TIME64.