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

in commit 22daaea3, 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.

src/ldso/__dlsym.c

@@ -8,3 +8,7 @@ static void *stub_dlsym(void *restrict p, const char *restrict s, void *restrict
 }
 
 weak_alias(stub_dlsym, __dlsym);
+
+#if _REDIR_TIME64
+weak_alias(stub_dlsym, __dlsym_redir_time64);
+#endif