Add a GitHub action for cross-compiling to MinGW via CMake.

.github/workflows/c-cpp.yml

@@ -17,3 +17,16 @@ jobs:
       run: ./configure
     - name: make
       run: make
+
+  build-cmake-mingw:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: apt
+      run: sudo apt-get install mingw-w64
+    - name: cmake
+      run: cmake -DCMAKE_TOOLCHAIN_FILE=i686-w64-mingw32.cmake .
+    - name: make
+      run: make

i686-w64-mingw32.cmake

@@ -0,0 +1,17 @@
+# CMake Toolchain file for cross-compiling PortAudio to i686-w64-mingw32
+# Inspired from: https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/cross_compiling/Mingw
+# Example usage: $ cmake -DCMAKE_TOOLCHAIN_FILE=i686-w64-mingw32.cmake .
+# i686-w64-mingw32 needs to be installed for this to work. On Debian-based
+# distributions the package is typically named `mingw-w64`.
+
+SET(CMAKE_SYSTEM_NAME Windows)
+
+SET(CMAKE_C_COMPILER i686-w64-mingw32-gcc)
+SET(CMAKE_CXX_COMPILER i686-w64-mingw32-g++)
+SET(CMAKE_RC_COMPILER i686-w64-mingw32-windres)
+
+SET(CMAKE_FIND_ROOT_PATH /usr/i686-w64-mingw32)
+
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)