Switch macOS static build to CMake (#1938)

This moves the tortuous flags out of our CI scripts,
and allows us to benefit from the libpng download caching.

.github/scripts/build_libpng.sh

@@ -1,23 +0,0 @@
-#!/bin/bash
-set -euo pipefail
-
-pngver=1.6.56
-
-## Grab sources and check them
-
-curl -LOJ "http://prdownloads.sourceforge.net/libpng/libpng-$pngver.tar.xz?download"
-echo f7d8bf1601b7804f583a254ab343a6549ca6cf27d255c302c47af2d9d36a6f18 \*libpng-$pngver.tar.xz | \
-	shasum -a 256 -c -
-
-## Extract sources and patch them
-
-tar -xvf libpng-$pngver.tar.xz
-
-## Start building!
-
-mkdir -p build
-cd build
-../libpng-$pngver/configure --disable-shared --enable-static \
-	CFLAGS="-O3 -flto -DNDEBUG -mmacosx-version-min=10.9 -arch x86_64 -arch arm64 -fno-exceptions"
-make -kj
-make install prefix="$PWD/../libpng-staging"

.github/workflows/create-release-artifacts.yml

@@ -54,13 +54,10 @@ jobs:
       - name: Install deps
         run: |
           ./.github/scripts/install_deps.sh macos
-      - name: Build libpng
-        run: |
-          ./.github/scripts/build_libpng.sh
-      # We force linking libpng statically; the other libs are provided by macOS itself
       - name: Build binaries
         run: |
-          make -kj CXXFLAGS="-O3 -flto -DNDEBUG -mmacosx-version-min=10.9 -arch x86_64 -arch arm64" PNGCFLAGS="-I libpng-staging/include" PNGLDLIBS="libpng-staging/lib/libpng.a -lz" Q=
+          cmake -S . -B build --preset macos-static -DFETCHCONTENT_BASE_DIR="${{ env.DEPS_ROOT_DIR }}"
+          cmake --build build
           strip rgb{asm,link,fix,gfx}
       - name: Package binaries
         run: |

.github/workflows/testing.yml

@@ -109,12 +109,16 @@ jobs:
       - name: Install deps
         run: |
           ./.github/scripts/install_deps.sh macos
-      - name: Build libpng
-        run: |
-          ./.github/scripts/build_libpng.sh
+      - name: Cache library deps
+        uses: actions/cache@v5
+        with:
+          path: ${{ env.DEPS_ROOT_DIR }}/*-tmp/
+          key: dep-srcs-${{ hashFiles('cmake/deps.cmake') }}
+          enableCrossOsArchive: true
       - name: Build & install
         run: |
-          make -kj CXXFLAGS="-O3 -flto -DNDEBUG -mmacosx-version-min=10.9 -arch x86_64 -arch arm64" PNGCFLAGS="-I libpng-staging/include" PNGLDLIBS="libpng-staging/lib/libpng.a -lz" Q=
+          cmake -S . -B build --preset macos-static -DFETCHCONTENT_BASE_DIR="${{ env.DEPS_ROOT_DIR }}"
+          cmake --build build
       - name: Package binaries
         run: |
           mkdir bins
@@ -168,7 +172,7 @@ jobs:
         with:
           path: ${{ env.DEPS_ROOT_DIR }}/*-tmp/
           key: dep-srcs-${{ hashFiles('cmake/deps.cmake') }}
-          enableCrossOsArchive: true # Currently only used on Windows, but the contents are OS-agnostic.
+          enableCrossOsArchive: true
       - name: Build Windows binaries
         run: | # ASan seems to be broken on Windows, so we disable it.
           cmake -S . -B build --preset develop-msvc${{ matrix.bits }} -DSANITIZERS=OFF \