libgcrypt: Configuration logfiles contain indications of -Wimplicit-function-declaration in "fn"

[judaew (Vadym-Valdis Yudaiev)]

--->  Configuring libgcrypt
Warning: Configuration logfiles contain indications of -Wimplicit-function-declaration; check that features were not accidentally disabled:
  fn: found in libgcrypt-1.10.0/config.log

[Schamschula (Marius Schamschula)]

Getting such an error may be intentional by the developer. In this case they are checking if the fn function is defined for the GCC assembler.

I'm not aware of a way of hiding theses messages.

[ryandesign (Ryan Carsten Schmidt)]

This check for fn occurs during "checking whether GCC assembler handles division correctly". The premise of the configure check seems faulty to me, since we are not using the GCC inline assembler. Perhaps the configure script should first ascertain whether the GCC inline assembler is being used, and only then perform more specific tests on it.

There are three ways of hiding these messages.

1. If the function being checked exists on macOS (or in an external library the project is trying to use), fix the code to include the header where that function is defined.
2. If the function being checked does not exist on macOS, add it to the global ignore files.
3. If the function being checked does exist on macOS but this portfile's build system is intentionally doing something weird and checking for its existence without including the right header (for example recent autoconf's check for strchr without including the right header in order to see how the compiler reacts to that), add the exclusion to the portfile itself by appending the function's name to configure.checks.implicit_function_declaration.whitelist.