AppVeyor: Also build with MinGW
diff --git a/appveyor.yml b/appveyor.yml
index c8e1a9d..4c64f29 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -1,14 +1,40 @@
 version: 1.0.{build}
 image: Visual Studio 2017
-build_script:
-- cmd: >-
-    call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
 
-    python configure.py --bootstrap
+environment:
+  CLICOLOR_FORCE: 1
+  CHERE_INVOKING: 1 # Tell Bash to inherit the current working directory
+  matrix:
+    - MSYSTEM: MINGW64
+    - MSYSTEM: MSVC
 
-    ninja.bootstrap.exe all
+for:
+  -
+    matrix:
+      only:
+        - MSYSTEM: MINGW64
+    build_script:
+      ps: "C:\\msys64\\usr\\bin\\bash -lc @\"\n
+      pacman -S --quiet --noconfirm --needed re2c 2>&1\n
+      sed -i 's|cmd /c $ar cqs $out.tmp $in && move /Y $out.tmp $out|$ar crs $out $in|g' configure.py\n
+      ./configure.py --bootstrap --platform mingw 2>&1\n
+      ./ninja all\n
+      ./ninja_test 2>&1\n
+      ./misc/ninja_syntax_test.py 2>&1\n\"@"
+  -
+    matrix:
+      only:
+        - MSYSTEM: MSVC
+    build_script:
+    - cmd: >-
+        call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
 
-    ninja_test
+        python configure.py --bootstrap
 
-    python misc/ninja_syntax_test.py
+        ninja.bootstrap.exe all
+
+        ninja_test
+
+        python misc/ninja_syntax_test.py
+
 test: off