✨️ A medley of CMake improvements

[ISSOtm]

Also bump it to the version I just tested it with

[Rangi42]

That's some abstruse ternary syntax, but sure.

[Rangi42]

Actually, it might be breaking in FreeBSD?

  Run command: bash -c 'cd /home/runner/work/rgbds/rgbds/test; ./fetch-test-deps.sh $<IF:$<BOOL:USE_NONFREE_TESTS>,,--only-free> $<IF:$<BOOL:USE_EXTERNAL_TESTS>,,--only-internal>'
  bash: -c: line 1: syntax error near unexpected token `newline'
  bash: -c: line 1: `cd /home/runner/work/rgbds/rgbds/test; ./fetch-test-deps.sh $<IF:$<BOOL:USE_NONFREE_TESTS>,,--only-free> $<IF:$<BOOL:USE_EXTERNAL_TESTS>,,--only-internal>'
  Problem running command: bash -c 'cd /home/runner/work/rgbds/rgbds/test; ./fetch-test-deps.sh $<IF:$<BOOL:USE_NONFREE_TESTS>,,--only-free> $<IF:$<BOOL:USE_EXTERNAL_TESTS>,,--only-internal>'
  Problem executing pre-test command(s).
  Errors while running CTest

I'd be fine with using ordinary ifs here.

[ISSOtm]

I agree this ternary synax looks a little icky, but I was trying to avoid five lines of conditional logic per option here, for readability. Tradeoffs tradeoffs...

[Rangi42]

These are long enough that they could be header-style not inline-style (like the comment on -Wno-gnu-zero-variadic-macro-arguments below):

Suggested change

	add_compile_options(
	/MP # Build multiple files in parallel.
	/wd5105 # MSVC's own standard library triggers warning C5105, "macro expansion producing 'defined' has undefined behavior".
	/wd5030 # Warning C5030 is about unknown attributes (`[[gnu::ATTR]]`), none of ours being load-bearing.
	/wd4996 # Warning C4996 is about using POSIX names, which we want to do for portability.
	/Zc:preprocessor # Opt into the C++20-conformant preprocessor.
	)
	add_compile_options(
	# Build multiple files in parallel
	/MP
	# MSVC's own standard library triggers warning C5105,
	# "macro expansion producing 'defined' has undefined behavior"
	/wd5105
	# Warning C5030 is about unknown attributes (`[[gnu::ATTR]]`),
	# none of ours being load-bearing.
	/wd5030
	# Warning C4996 is about using POSIX names,
	# which we want to do for portability.
	/wd4996
	# Opt into the C++20-conformant preprocessor.
	/Zc:preprocessor
	)

[ISSOtm]

Since the CMakeLists is quite long, I was trying to keep it more compact. But if you think that this is nonetheless better, I'd be fine with you committing this.