222 from Sean Cross. Corrected a few places where the blanket
conversion "Region"->"ExtRegion" picked up some comment lines
that were unrelated to the structure name.
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.