ci: Exclude mpexamples in openbsd build for now

Due to link error:

[54/59] Linking CXX executable example/mpexample
FAILED: example/mpexample
: && /usr/bin/c++ -Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -Xlinker --dependency-file=example/CMakeFiles/mpexample.dir/link.d example/CMakeFiles/mpexample.dir/example.cpp.o example/CMakeFiles/mpexample.dir/init.capnp.c++.o example/CMakeFiles/mpexample.dir/init.capnp.proxy-client.c++.o example/CMakeFiles/mpexample.dir/init.capnp.proxy-server.c++.o example/CMakeFiles/mpexample.dir/init.capnp.proxy-types.c++.o example/CMakeFiles/mpexample.dir/calculator.capnp.c++.o example/CMakeFiles/mpexample.dir/calculator.capnp.proxy-client.c++.o example/CMakeFiles/mpexample.dir/calculator.capnp.proxy-server.c++.o example/CMakeFiles/mpexample.dir/calculator.capnp.proxy-types.c++.o example/CMakeFiles/mpexample.dir/printer.capnp.c++.o example/CMakeFiles/mpexample.dir/printer.capnp.proxy-client.c++.o example/CMakeFiles/mpexample.dir/printer.capnp.proxy-server.c++.o example/CMakeFiles/mpexample.dir/printer.capnp.proxy-types.c++.o -o example/mpexample  libmultiprocess.a  -lstdc++fs  /usr/local/lib/libcapnp-rpc.a  /usr/local/lib/libcapnp.a  /usr/local/lib/libkj-async.a  /usr/local/lib/libkj.a  -lpthread  -Wl,-rpath-link,/usr/X11R6/lib:/usr/local/lib && :
ld: error: unable to find library -lstdc++fs
c++: error: linker command failed with exit code 1 (use -v to see invocation)

Author: marco

ci/configs/openbsd.bash

@@ -1,5 +1,6 @@
 CI_DESC="CI config for OpenBSD"
 CI_DIR=build-openbsd
+BUILD_TARGETS=(all tests)  # Exclude mpexamples for now
 export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter"
 CMAKE_ARGS=(-G Ninja)
 BUILD_ARGS=(-k 0)