surprisingly, they were actually harmless because ndk builds with

--gc-sections, which eliminates unused code and thus obviates the
undefined symbol

openssh/misc.c

@@ -76,6 +76,8 @@ chop(char *s)
 
 }
 
+#if 0 /* unused, and calls undefined debug() */
+
 /* set/unset filedescriptor to non-blocking */
 int
 set_nonblock(int fd)
@@ -697,6 +699,8 @@ tun_open(int tun, int mode)
 #endif
 }
 
+#endif /* 0 */
+
 void
 sanitise_stdfd(void)
 {
@@ -720,6 +724,8 @@ sanitise_stdfd(void)
 		close(nullfd);
 }
 
+#if 0 /* unused, and calls undefined debug() */
+
 char *
 tohex(const void *vp, size_t l)
 {
@@ -757,6 +763,8 @@ get_u64(const void *vp)
 	return (v);
 }
 
+#endif /* 0 */
+
 u_int32_t
 get_u32(const void *vp)
 {
@@ -843,6 +851,8 @@ put_u16(void *vp, u_int16_t v)
 	p[1] = (u_char)v & 0xff;
 }
 
+#if 0 /* unused, and calls undefined debug() */
+
 void
 ms_subtract_diff(struct timeval *start, int *ms)
 {
@@ -1097,3 +1107,4 @@ sock_set_v6only(int s)
 		error("setsockopt IPV6_V6ONLY: %s", strerror(errno));
 #endif
 }
+#endif /* 0 */