slint-dev.sh / slint-dev-fast.sh assume a Linux toolchain (mold linker,
x86 AES-NI features). On macOS clang rejects -fuse-ld=mold and the build
fails at the first link. This adds slint-dev-mac.sh: same nightly parallel
frontend and release-by-default intent, with --fast for a quick debug
build, the AES-NI/SSSE3 features scoped to x86_64 only, and the default
Apple linker (ld-prime). Verified on Apple Silicon: builds, runs, plays audio.
