CI: Add build-tests for various compilers on Windows and Ubuntu

The build setup for this repository is incredibly simple, but
unfortunately even recent changes to the CMake have made various
platforms and compiler combinations unbuildable.  Add a basic CI that at
the very least _builds_ the project to demonstrate all these problems,
which should all go away when other PRs are merged.

Author: MarijnS95

.github/workflows/ci.yaml

@@ -0,0 +1,47 @@
+on:
+  - push
+
+jobs:
+  build-linux:
+    name: Use clang and gcc via "Unix Makefiles"
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        compiler: [clang, gcc]
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          cmake -Bbuild -DCMAKE_C_COMPILER=${{ matrix.compiler }}
+          cmake --build build
+
+  build-windows-ninja:
+    name: Use clang and clang-cl via Ninja
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        # On Windows, clang only enables the WIN32 flag in CMake whereas
+        # clang-cl also enables MSVC, because it has a cl.exe-like interface.
+        compiler: [clang, clang-cl]
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          # Use Ninja because the MSBuild toolchain can only configure
+          # alternative compilers via "toolsets", where only ClangCL is
+          # supported.
+          cmake -Bbuild -GNinja -DCMAKE_C_COMPILER=${{ matrix.compiler }}
+          cmake --build build
+
+  build-windows-msbuild:
+    name: Use MSVC and clang-cl via MSBuild
+    runs-on: windows-latest
+    strategy:
+      matrix:
+        toolset:
+          # The default toolset should be the latest 'v143' when nothing is specified
+          -
+          - -TClangCL
+    steps:
+      - uses: actions/checkout@v4
+      - run: |
+          cmake -Bbuild ${{ matrix.toolset }}
+          cmake --build build

Makefile

@@ -72,12 +72,11 @@ ifneq ($(shared), not-set)
 endif
 
 define run-config
-mkdir -p $(BUILDDIR)
-cd $(BUILDDIR) && cmake $(CURDIR) $(CONFIG_FLAGS)
+cmake $(CURDIR) -B"$(BUILDDIR)" $(CONFIG_FLAGS)
 endef
 
 all clean install: $(BUILDDIR)
-	make -C $(BUILDDIR) $@
+	cmake --build $(BUILDDIR) $@
 
 uninstall:
 	 xargs rm < $(BUILDDIR)/install_manifest.txt