Building in 8.1.10.RC 2 for iOS - Missing Undefined symbols

Tue May 15 23:00:04 EDT 2018

I just downloaded 8.1.10 RC 2

I have both xCode 9.2 and 9.3 entered in preferences. I get a "green" OK in the standalone preferences.

But when I try to build for iOS , I get

======
[error]

Unable to build app for device: linking for arm (arm64) failed with Undefined symbol for
architecture arm 64

"_pthread_key_delete",referenced from:
    |4092 in revsecurity

# and whole series like this
# see screenshot here

http://wiki.hindu.org/screenshots/2018-05-15_16-46-45.jpeg

What to do?