FYI: Recently fixed build system issues

[pcarruscag]

Some small issues resulting from recent file restructurings and PR's are already fixed in #824 and can be merged with #843 and #849 (no need for anyone else to fix them). Namely:

• Updated legacy build system;
• Meson with cgns disabled;
• IDE-friendly include paths (with all the ../ required);
• Compiler warnings addressed.

[pcarruscag]

Another one, you may have noticed the build times going up with the file restructurings we have been doing. Fear not, solution and explanation are in #824