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A clear and concise description of what the bug is.

I get the following error using gcc 11.3.0 on cygwin:

/cygdrive/c/projects/clingo/third_party/catch/src/catch2/../catch2/catch_tostring.hpp:214:33: error: there are no arguments to 'strnlen' that depend on a template parameter, so a declaration of 'strnlen' must be available [-fpermissive]
  214 |                 StringRef( str, strnlen( str, SZ ) ) );

What about using strnlen_s instead? The only problem I see is that additional macros would have to be defined but since the templates are fully instantiated, the required code could be moved to the source file.

There might also be another header providing a strnlen. I could dig a little deeper if help is required.

Platform information:

• OS: Windows + Cygwin
• Compiler+version: GCC v11.3.0
• Catch version: v3.1.0