Alessandro De Laurenzis. That pull request cleaned up the vast
majority of compiler warnings. However, that cleanup exposed a
few additional warnings pointing to errors in the code that needed
fixing. The code now compiles cleanly except for one warning
about redefined CAD_DIR that I have not looked into.
This commit makes the code (mostly) C99-compatible, enabling to compile
it without the -Wno-error=implicit-function-declaration flag. This
way, Magic becomes usable on arm64 architectures, specifically on Apple
computers with M1/M2 SoC.