build: Refactor appveyor/Windows scripts (#5244)

- Join all msys build scripts into one
- Clean up appveyor.yml and generate installer for tagged builds

A side effect of the cosmetic changes is that appveyor artifact
permalinks are easier to use, e.g. for the latest zip in the
master branch

    https://ci.appveyor.com/api/projects/neovim/neovim/artifacts/build/Neovim.zip?branch=master&job=Configuration%3A%20MINGW_64

.ci/msys_build_deps.bat → .ci/build.bat

@@ -2,7 +2,7 @@
 :: MSYS2, this allows using all the dependencies and tools available
 :: in MSYS2, but we cannot build inside the MSYS2 shell.
 echo on
-if "%TARGET%" == "MINGW_32" (
+if "%CONFIGURATION%" == "MINGW_32" (
 	set ARCH=i686
 	set BITS=32
 ) else (
@@ -12,7 +12,10 @@ if "%TARGET%" == "MINGW_32" (
 :: We cannot have sh.exe in the PATH (MinGW)
 set PATH=%PATH:C:\Program Files\Git\usr\bin;=%
 set PATH=C:\msys64\mingw%BITS%\bin;C:\Windows\System32;C:\Windows;%PATH%
+:: The default cpack in the PATH is not CMake
+set PATH=C:\Program Files (x86)\CMake\bin\cpack.exe;%PATH%
 
+:: Build third-party dependencies
 C:\msys64\usr\bin\bash -lc "pacman --verbose --noconfirm -Su" || goto :error
 C:\msys64\usr\bin\bash -lc "pacman --verbose --noconfirm --needed -S mingw-w64-%ARCH%-cmake mingw-w64-%ARCH%-perl mingw-w64-%ARCH%-python2 mingw-w64-%ARCH%-diffutils" || goto :error
 
@@ -22,6 +25,19 @@ cmake -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release ..\third-party\ || goto :e
 mingw32-make VERBOSE=1 || goto :error
 cd ..
 
+:: Build Neovim
+mkdir build
+cd build
+cmake -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release .. || goto :error
+mingw32-make VERBOSE=1 || goto :error
+bin\nvim --version || goto :error
+cd ..
+
+:: Build artifacts
+cd build
+cpack -G ZIP -C Release
+if defined APPVEYOR_REPO_TAG_NAME cpack -G NSIS -C Release
+
 goto :EOF
 :error
 exit /b %errorlevel%

.ci/msys_build.bat

-echo on
-if "%TARGET%" == "MINGW_32" (
-	set ARCH=i686
-	set BITS=32
-) else (
-	set ARCH=x86_64
-	set BITS=64
-)
-:: We cannot have sh.exe in the PATH (MinGW)
-set PATH=%PATH:C:\Program Files\Git\usr\bin;=%
-set PATH=C:\msys64\mingw%BITS%\bin;C:\Windows\System32;C:\Windows;%PATH%
-
-mkdir build
-cd build
-cmake -G "MinGW Makefiles" -DCMAKE_BUILD_TYPE=Release .. || goto :error
-mingw32-make VERBOSE=1 || goto :error
-bin\nvim --version || goto :error
-cd ..
-
-goto :EOF
-:error
-exit /b %errorlevel%

appveyor.yml

 version: '{build}'
-skip_tags: true
-environment:
-  # The default cpack in the PATH is not CMake
-  CPACK: C:\Program Files (x86)\CMake\bin\cpack.exe
-  matrix:
-  - TARGET: MINGW_64
-    BUILD_DEPS_SCRIPT: .ci\msys_build_deps.bat
-    BUILD_SCRIPT: .ci\msys_build.bat
-  - TARGET: MINGW_32
-    BUILD_DEPS_SCRIPT: .ci\msys_build_deps.bat
-    BUILD_SCRIPT: .ci\msys_build.bat
+configuration:
+- MINGW_64
+- MINGW_32
 install: []
 build_script:
-- if defined BUILD_DEPS_SCRIPT call %BUILD_DEPS_SCRIPT%
-- call %BUILD_SCRIPT%
-# Build artifacts
-- cd build
-- '"%CPACK%" -G NSIS -C Release'
-- '"%CPACK%" -G ZIP -C Release'
+- call .ci\build.bat
 artifacts:
 - path: build/Neovim.zip
+- path: build/Neovim.exe