bug#42702: catch2 build failure on ARM

[maxim.cournoyer@gmail.com]

maxim.cournoyer@gmail.com writes:

> On ARM systems, (armhf-linux, aarch64-linux), the catch2 package fails to build, due to a
> compilation warning treated as an error:
>
> [ 90%] Building CXX object CMakeFiles/SelfTest.dir/include/reporters/catch_reporter_xml.cpp.o
> /gnu/store/ap7hgyv4rjqmhg4a6cb6cypsh3g1f5q4-gcc-7.5.0/bin/c++   -I/tmp/guix-build-catch2-2.1.2.drv-0/source/include  -O2 -g -DNDEBUG   -Wall -Wextra -Wunreachable-code -Wpedantic -Werror -std=c++11 -o CMakeFiles/SelfTest.dir/include/reporters/catch_reporter_xml.cpp.o -c /tmp/guix-build-catch2-2.1.2.drv-0/source/include/reporters/catch_reporter_xml.cpp
> /tmp/guix-build-catch2-2.1.2.drv-0/source/include/internal/catch_tostring.cpp: In static member function ‘static std::__cxx11::string Catch::StringMaker<char>::convert(char)’:
> /tmp/guix-build-catch2-2.1.2.drv-0/source/include/internal/catch_tostring.cpp:202:21: error: comparison is always true due to limited range of data type [-Werror=type-limits]
>      } else if ('\0' <= value && value < ' ') {
>                 ~~~~~^~~~~~~~

This is also the case for i686-linux.