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.
polygon cell has been created with the "gds polygon subcell"
option and the parent cell is read-only (vendor GDS), then the
polygon cell does not actually exist in the original GDS and
should not be output during a "gds write".
Compression levels of the output can be controlled with the "gds
compress [<value>]" command, where <value> 0 (default) is uncompressed
output, 6 is "normal" gzip compression, and 9 is maximum compression.
Alessandro De Laurenzis
Tim Edwards