appveyor.yml, appveyor.cmd: Initial attempt to add support for MinGW-w64 on AppVeyor.

This uses a new matrix configuration with platform, configuration,
and compiler. Note that we're only testing debug builds with MinGW-w64
for now.

Notes:

- git has to be removed from the path. Otherwise, cmake thinks that it's
  running from a UNIX shell, which requires MSYS Makefiles.
  - Reference: https://help.appveyor.com/discussions/problems/3193-cmake-building-for-mingw-issue-with-git-shexe
  - Note that git is 64-bit in AppVeyor now, and sh is in usr/bin/. I'm
    checking for all four configurations.

- Build in a build/ subdirectory in all configurations.

- MSVC configurations are temporarily disabled so we can fix all MinGW-w64
  issues without having to wait for the MSVC builds to finish.

- The VS2013 image has MinGW-w64 x86_64 7.2.0, not 8.1.0.
  The AppVeyor documentation is incorrect.

appveyor.cmd

@@ -1,7 +1,31 @@
 @ECHO OFF
 cmake --version
-IF "%PLATFORM%" == "x64" (
-	cmake . -G "Visual Studio 12 2013 Win64" -DCMAKE_GENERATOR_TOOLSET=v120_xp -DENABLE_JPEG=ON -DBUILD_TESTING=ON -DENABLE_LTO=OFF -DENABLE_PCH=ON
-) ELSE (
-	cmake . -G "Visual Studio 12 2013" -DCMAKE_GENERATOR_TOOLSET=v120_xp -DENABLE_JPEG=ON -DBUILD_TESTING=ON -DENABLE_LTO=OFF -DENABLE_PCH=ON
-)
+
+if "%compiler%" == "msvc2013" goto :msvc2013
+if "%compiler%" == "mingw-w64" goto :mingw-w64
+echo *** ERROR: Unsupported compiler '%compiler%'.
+exit /b 1
+
+:msvc2013
+set PreferredToolArchitecture=x64
+set "CMAKE_GENERATOR=Visual Studio 12 2013"
+set CMAKE_GENERATOR_TOOLSET=v120_xp
+if "%platform%" == "x64" set "CMAKE_GENERATOR=%CMAKE_GENERATOR% Win64"
+mkdir build
+cd build
+cmake .. -G "%CMAKE_GENERATOR%" -DCMAKE_GENERATOR_TOOLSET=%CMAKE_GENERATOR_TOOLSET% -DENABLE_JPEG=ON -DBUILD_TESTING=ON -DENABLE_LTO=OFF -DENABLE_PCH=ON
+exit /b %ERRORLEVEL%
+
+:mingw-w64
+set PATH=%PATH:C:\Program Files\Git\bin;=%
+set PATH=%PATH:C:\Program Files\Git\usr\bin;=%
+set PATH=%PATH:C:\Program Files (x86)\Git\bin;=%
+set PATH=%PATH:C:\Program Files (x86)\Git\usr\bin;=%
+if "%platform%" == "x86" set MINGW64_ROOT=C:/mingw-w64/i686-6.3.0-posix-dwarf-rt_v5-rev1/mingw32
+if "%platform%" == "x64" set MINGW64_ROOT=C:/mingw-w64/x86_64-7.2.0-posix-seh-rt_v5-rev1/mingw64
+set "PATH=%MINGW64_ROOT%\bin;%PATH%"
+
+mkdir build
+cd build
+cmake .. -G "MinGW Makefiles" -DCMAKE_PREFIX_PATH=%MINGW64_ROOT% -DCMAKE_C_COMPILER=%MINGW64_ROOT%/bin/gcc.exe -DCMAKE_CXX_COMPILER=%MINGW64_ROOT%/bin/g++.exe -DCMAKE_BUILD_TYPE=%configuration% -DENABLE_JPEG=ON -DBUILD_TESTING=ON -DENABLE_LTO=OFF -DENABLE_PCH=ON
+exit /b %ERRORLEVEL%

appveyor.yml

@@ -22,13 +22,31 @@ only_commits:
     - extlib/**/*
     - src/**/*
 
-platform:
-  - x86
-  - x64
+environment:
+  matrix:
+    #- platform: x86
+    #  configuration: Debug
+    #  compiler: msvc2013
 
-configuration:
-  - Debug
-  - Release
+    #- platform: x86
+    #  configuration: Release
+    #  compiler: msvc2013
+
+    #- platform: x64
+    #  configuration: Debug
+    #  compiler: msvc2013
+
+    #- platform: x64
+    #  configuration: Release
+    #  compiler: msvc2013
+
+    - platform: x86
+      configuration: Debug
+      compiler: mingw-w64
+
+    - platform: x64
+      configuration: Debug
+      compiler: mingw-w64
 
 # Run CMake.
 before_build:
@@ -36,11 +54,11 @@ before_build:
   - appveyor.cmd
 
 build_script:
-  - cd %APPVEYOR_BUILD_FOLDER%
-  - msbuild ALL_BUILD.vcxproj
+  - cd %APPVEYOR_BUILD_FOLDER%\build
+  - cmake --build . --config %configuration%
 
 test_script:
-  - cd %APPVEYOR_BUILD_FOLDER%
-  - ctest -V -C %CONFIGURATION%
+  - cd %APPVEYOR_BUILD_FOLDER%\build
+  - ctest -V -C %configuration%
 
 # TODO: Automatic packaging?