CI: test on MinGW

This should extend testing to Lwt's Win32 code.

The testing scripts ultimately use fdopen's OCaml for Windows. See
https://fdopen.github.io/opam-repository-mingw/

Part of #249.

appveyor.yml

@@ -3,21 +3,20 @@ version: "{build}"
 shallow_clone: true
 
 environment:
-  global:
-    CYGWIN: C:\Cygwin
-    CYGSH: C:\Cygwin\bin\bash -lc
   matrix:
-    - {SYSTEM: cygwin, COMPILER: 4.01}
-    - {SYSTEM: cygwin, COMPILER: 4.02}
+    - {SYSTEM: cygwin, ARCH: x86, COMPILER: 4.01}
+    - {SYSTEM: cygwin, ARCH: x86, COMPILER: 4.02}
+    - {SYSTEM: mingw, ARCH: x86_64, COMPILER: 4.03}
 
 install:
-  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/x86/ocaml/$env:COMPILER/install.ps1") | PowerShell -Command -'
-  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/x86/camlp4/$env:COMPILER/install.ps1") | PowerShell -Command -'
-  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/x86/opam/1.2/install.ps1") | PowerShell -Command -'
-  - '%CYGSH% "cd /cygdrive/c/projects/lwt ; utils/appveyor-%SYSTEM%-install.sh"'
+  - 'IF "%ARCH%"=="x86" ( SET CYGSH=C:\Cygwin\bin\bash -lc ) ELSE ( SET CYGSH=C:\Cygwin64\bin\bash -lc )'
+  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/$env:ARCH/ocaml/$env:COMPILER/install.ps1") | PowerShell -Command -'
+  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/$env:ARCH/camlp4/$env:COMPILER/install.ps1") | PowerShell -Command -'
+  - ps: '(new-object net.webclient).DownloadString("https://aantron.github.io/binaries/$env:SYSTEM/$env:ARCH/opam/1.2/install.ps1") | PowerShell -Command -'
+  - '%CYGSH% "cd /cygdrive/c/projects/lwt ; utils/appveyor-cygwin-install.sh"'
 
 build_script:
-  - '%CYGSH% "cd /cygdrive/c/projects/lwt ; utils/appveyor-%SYSTEM%-build.sh"'
+  - '%CYGSH% "cd /cygdrive/c/projects/lwt ; utils/appveyor-cygwin-build.sh"'
 
 cache:
-  - '..\opam-cache-%COMPILER%.tar -> opam, appveyor.yml, utils\appveyor*.sh'
+  - '..\opam-cache-%SYSTEM%-%COMPILER%.tar -> opam, appveyor.yml, utils\appveyor*.sh'

utils/appveyor-cygwin-install.sh

@@ -7,7 +7,7 @@ DIRECTORY=$(pwd)
 
 # AppVeyor does not cache empty subdirectories of .opam, such as $SWITCH/build.
 # To get around that, create a tar archive of .opam.
-CACHE=$DIRECTORY/../opam-cache-$COMPILER.tar
+CACHE=$DIRECTORY/../opam-cache-$SYSTEM-$COMPILER.tar
 
 if [ ! -f $CACHE ]
 then