math/tblis: unbreak with libc++ 8

In file included from src/iface/1v/add.cxx:1:
In file included from src/iface/1v/add.h:4:
In file included from src/iface/1v/../../util/thread.h:10:
In file included from ./src/external/tci/tci.h:4:
In file included from ./src/external/tci/tci/barrier.h:7:
In file included from src/external/tci/tci/mutex.h:50:
In file included from /usr/include/c++/v1/system_error:147:
In file included from /usr/include/c++/v1/type_traits:406:
In file included from /usr/include/c++/v1/cstddef:38:
./version:1:1: error: expected unqualified-id
1.0.0
^

PR: 236192
Approved by: portmgr blanket