libobjc2 on OpenBSD 6.8 build errors - C++ runtime not found

Hi,

while I need to find some time to reply about NetBSD issues, I wanted to 
test current  base/gui/back on OpenBSD before our release and as I was 
also test latest libobjc2. Since I had pending to upgraded to latest 
OpenBSD 6.8, I did that too.

Before upgrading, I did build libobjc2 on 6.7 which had an older clang: 
it did build and 95% of the test passed (the failures being similar to 
NetBSD/amd64 btw). After that I proceeded upgrading my system, userland, 
packages and restarted building libobjc2.

I get this failure during build:

Scanning dependencies of target CXXExceptions_legacy_optimised
[  9%] Building C object 
Test/CMakeFiles/CXXExceptions_legacy_optimised.dir/CXXException.m.o
[ 10%] Building CXX object 
Test/CMakeFiles/CXXExceptions_legacy_optimised.dir/CXXException.cc.o
[ 10%] Linking C executable CXXExceptions_legacy_optimised
ld: error: /home/multix/code/gnustep-cvs/libobjc2/Build/libobjc.so: 
undefined reference to cxx_throw()
ld: error: /home/multix/code/gnustep-cvs/libobjc2/Build/libobjc.so: 
undefined reference to test_eh_personality
cc: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[2]: *** 
[Test/CMakeFiles/CXXExceptions_legacy_optimised.dir/build.make:123: 
Test/CXXExceptions_legacy_optimised] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:558: 
Test/CMakeFiles/CXXExceptions_legacy_optimised.dir/all] Error 2
gmake: *** [Makefile:183: all] Error 2


(which, if memory serves me, was one of the tests failing on 6.7, but at 
leaste everything compiled)

I am suspicious that I do not find the CXX_RUNTIME_LIB set by cmake.

While runing cmake, I saw this:

-- Testing C++ interop
-- Testing /usr/lib/libsupc++.a as the C++ runtime library
-- Testing /usr/lib/libc++abi.so.3.0 as the C++ runtime library
-- Testing C++ standard library
-- Using /usr/bin/cc
-- No useable C++ runtime found


why doesn't it like my runtime library?

Riccardo