mprime fail to start on FreeBSD 12 with clang - why!?

[Rozhuk Ivan]

Hello!

I maintain math/mprime.

It can not start on FreeBSD 12 if it build with clang.
If works ok on 11.2.
Both 11.2 and 12.0 stable, updated less than 1m ago - same clang version.

If it build with gcc8 - it does not depend on gcc runtime, gcc can be
removed and mprime continue work.
To build with gcc: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=236546

Why this can happen?