Add missing sign for cppcheck --template argument

[eht16]

Closes #1304.

[eht16]

@elextr I couldn't resist to credit this great and very sophisticated change to you as you already solved the mystery in #1304 (comment)!

[elextr]

I just RTFineM for cppcheck, but I don't use it, so thats why I referred it to @b4n who wrote it originally or anybody else who has a new enough version that --template is an official option, not UU (undocumented unofficial).

[elextr]

@eht16, To perhaps be more clear, I don't have a new enough cppcheck to test this, but if it works for you, approved, although I'm not sure why the output format needs to be forced to some specific format.

[eht16]

I tested the --template=gcc format locally with the latest cppcheck version and it works.

The idea by using the specific "gcc" template was probably that the output can be parsed by Geany out of the box using the default error message regex for C/C++ files. But this is just a guess.

I noticed new "undefined macro" errors while testing and added those as well (same story as in #1196).

With these changes, "make check" ran fine on my system.

[eht16]

See also #1310 for an improved CI build with using the current "cppcheck" version instead of the dated version from the CI runner image.