The compiler runs on Windows (and has seeds for macOS)

Windows: the compiler made from bootstrap/windows-x86_64.ll runs under Wine, compiles itself to the same IR, builds an
exe of itself, and every test program passes through it. It needed: Windows-sized unsigned long for libclang's unsaved
file, no 'cross' when Windows builds for Windows, --target passed to libclang (libclang.dll assumes MSVC), the MinGW
triple always in the IR, FINCH_LDFLAGS, .exe names and FINCH_LLVM_INCLUDE in bootstrap/build.sh, winseed.sh/winbuild.sh.
macOS: seeds for arm64 and x86-64 made with the 11.3 SDK; IR is accepted by clang, nothing has run on a Mac yet.
CI gets a windows and a macos job. UNTESTED on real Windows/macOS runners.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015f73FesGZGYPkmDvUcj6QX

.github/workflows/ci.yml

@@ -1,8 +1,8 @@
 name: CI
 
 # The compiler is written in Finch. It is built from bootstrap/<system>.ll, its own LLVM IR (see bootstrap/README.md),
-# then from itself. Linux x86-64 and ARM64 have seeds; macOS and Windows machines can't build the compiler yet
-# (programs for them are built from Linux with --target, and tested here under Wine and qemu).
+# then from itself. Seeds: Linux x86-64 and ARM64 (tested here), Windows x86-64 (tested under Wine, and here),
+# macOS ARM64 and x86-64 (made with Apple's headers; only checked as IR until the macos job below passes).
 
 on:
   push:
@@ -74,6 +74,49 @@ jobs:
             FINCH_CC=aarch64-linux-gnu-gcc QEMU_LD_PREFIX=/usr/aarch64-linux-gnu tests/cross.sh arm64
           fi
 
+  macos:
+    runs-on: macos-15
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install LLVM 21 (libclang)
+        run: brew install llvm@21 pkg-config
+      - name: Build the compiler
+        run: |
+          export FINCH_CLANG="$(brew --prefix llvm@21)/bin/clang"
+          export FINCH_LIBCLANG="-L$(brew --prefix llvm@21)/lib -lclang"
+          export FINCH_LLVM_INCLUDE="$(brew --prefix llvm@21)/include"
+          bootstrap/build.sh
+          build/finch version
+      - name: Tests
+        run: tests/run.sh
+
+  windows:
+    runs-on: windows-2022
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - uses: actions/checkout@v4
+      - name: Download llvm-mingw (clang with MinGW headers) and LLVM for Windows (libclang.dll)
+        run: |
+          curl -sSL -o mingw.zip https://github.com/mstorsjo/llvm-mingw/releases/download/20251216/llvm-mingw-20251216-ucrt-x86_64.zip
+          7z x -y mingw.zip -o/c/ > /dev/null
+          curl -sSL -o llvm.exe https://github.com/llvm/llvm-project/releases/download/llvmorg-21.1.8/LLVM-21.1.8-win64.exe
+          7z x -y llvm.exe -o/c/llvm > /dev/null
+      - name: Build the compiler
+        run: |
+          export PATH="/c/llvm-mingw-20251216-ucrt-x86_64/bin:$PATH"
+          export FINCH_LIBCLANG="C:/llvm/bin/libclang.dll"
+          export FINCH_LLVM_INCLUDE="C:/llvm/include"
+          export FINCH_LDFLAGS="-LC:/llvm/bin"
+          bootstrap/build.sh
+          build/finch.exe version
+      - name: Tests
+        run: |
+          export PATH="/c/llvm-mingw-20251216-ucrt-x86_64/bin:$PATH"
+          export FINCH_LDFLAGS="-LC:/llvm/bin"
+          FINCH=../build/finch.exe tests/run.sh
+
   vscode:
     runs-on: ubuntu-24.04
     defaults: