Relevant part (hopefully):
g++ -c -o out/issue122.o test/t/issue122.cpp -Iinclude -isystem test/include -std=c++11 -Werror -Wall -Wextra -pedantic -Wformat=2 -Wsign-conversion -Wshadow -Wunused-parameter -O3 -DNDEBUG -march=native -DSINGLE_THREADED -fvisibility-inlines-hidden -fvisibility=hidden -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -pthread
In file included from /usr/include/signal.h:328,
from test/include/catch.hpp:6392,
from test/unit.cpp:2:
test/include/catch.hpp:6415:33: error: size of array ‘altStackMem’ is not an integral constant-expression
6415 | static char altStackMem[SIGSTKSZ];
| ^~~~~~~~
test/include/catch.hpp:6466:45: error: size of array ‘altStackMem’ is not an integral constant-expression
6466 | char FatalConditionHandler::altStackMem[SIGSTKSZ] = {};
| ^~~~~~~~
mkdir -p ./out
g++ -c -o out/mutating_visitor.o test/t/mutating_visitor.cpp -Iinclude -isystem test/include -std=c++11 -Werror -Wall -Wextra -pedantic -Wformat=2 -Wsign-conversion -Wshadow -Wunused-parameter -O3 -DNDEBUG -march=native -DSINGLE_THREADED -fvisibility-inlines-hidden -fvisibility=hidden -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -pthread
make[1]: *** [Makefile:96: out/unit.o] Error 1
As reported in Debian Bug #1017327: