The vast majority of this is fixing up `char *` that should be `const char *`
but a handful of other fixes, like potential buffer overflows that GCC
noticed, etc, were applied as well.
This removes `-Wno-write-strings` from CMakeLists.txt, as it is no longer
necessary, as there is no longer a flood of compiler warning spam when
building.
This does not fix all compiler warnings; there are still a handful, and they
are legitimate, but they can be dealt with in a future commit.
At this point, all remaining references to `MACINTOSH` are either part
of multi-value conditionals that `unifdef` was unable to determine the
final value for, or a `#define`, or a comment. I manually go through the
files with a Ctrl+Shift+F search (ignoring legacy/, to preserve useful
historic knowledge) and clean up each usage.
As part of that search, I discovered `lib/mac/` which I deleted wholly.
Test Plan:
On Mac, build both Debug and Release
```
cmake --build --preset mac --config Debug
cmake --build --preset mac --config Release
```
