Fix CI 32 build failure in GCC

And update appveyor.yml and BUILD.md to reflect the migration to MSYS2

Fix #12447, close #12450, close #12481

BUILD.md

@@ -48,11 +48,11 @@ uses features from Boost's `Boost.Regex` library.
 
 # Building Notepad++ with GCC
 
-If you have [MinGW-w64](https://www.mingw-w64.org/) installed, you can compile Notepad++ with GCC.
+If you have [MinGW-w64](https://www.mingw-w64.org/) installed, you can compile Notepad++ with GCC. Otherwise MinGW-w64 can be downloaded [here](https://sourceforge.net/projects/mingw-w64/files/).  You can also download some collection of tools which supports MinGW-w64, like [MSYS2](https://www.msys2.org/) or [WinLibs](https://winlibs.com/).
 
-MinGW-w64 can be downloaded [here](https://sourceforge.net/projects/mingw-w64/files/). Building Notepad++ is regularly tested on a Windows system with [x86_64-8.1.0-release-posix-seh-rt_v6-rev0](https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/8.1.0/threads-posix/seh/x86_64-8.1.0-release-posix-seh-rt_v6-rev0.7z) for building 64-bits binary and with [i686-8.1.0-release-posix-dwarf-rt_v6-rev0](https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win32/Personal%20Builds/mingw-builds/8.1.0/threads-posix/dwarf/i686-8.1.0-release-posix-dwarf-rt_v6-rev0.7z) versions for building 32-bits binary. Other versions may also work but are untested.
+Building Notepad++ is regularly tested on a Windows system by using  [MSYS2](https://www.msys2.org/) project.  Current versions of tools  used to building (such as GCC, Make or Bash) can be checked by looking at some logos from the finished building (for example in the [current-build page](https://ci.appveyor.com/project/donho/notepad-plus-plus)). Other versions may also work but are untested.
 
-**Note:** If you use MinGW-w64 GCC from a package (7z), you need to manually add the `$MinGW-root$\bin` directory to the system `PATH` environment variable for the `mingw32-make` invocation below to work. One can use a command like `set PATH=$MinGW-root$\bin;%PATH%` each time `cmd` is launched. But beware that if `PATH` contains several versions of MinGW-w64 GCC, only the first one will be usable.
+**Note:** Before building make sure that the system `PATH` environment variable contains `$MinGW-root$\bin` directory. Otherwise you have to set this directory yourself in Windows settings. You can also use a command like `set PATH=$MinGW-root$\bin;%PATH%` each time `cmd` is launched. But beware that if `PATH` contains several versions of MinGW-w64 GCC, only the first one will be usable.
 
 ## Compiling Notepad++ binary
 

appveyor.yml

@@ -29,9 +29,11 @@ configuration:
 
 before_build:
     - ps: |
+        Write-Output "Build parameters:"
         Write-Output "Compiler : $env:compiler"
         Write-Output "Platform : $env:platform"
         Write-Output "Configuration : $env:configuration"
+        Write-Output ""
 
 for:
 - matrix:
@@ -93,19 +95,23 @@ for:
     only:
       - compiler: GCC
   install:
-    - set PATH=C:\msys64\usr\bin
-    - if "%platform%" EQU "i686" set $env:MSYSTEM = 'MINGW32'
-    - if "%platform%" EQU "x86_64" set $env:MSYSTEM = 'MINGW64'
+    - set PATH=C:\msys64\usr\bin;%PATH%
+    - if "%platform%" EQU "i686" set MSYSTEM=MINGW32 && set PATH=C:\msys64\mingw32\bin;%PATH%
+    - if "%platform%" EQU "x86_64" set MSYSTEM=MINGW64 && set PATH=C:\msys64\mingw64\bin;%PATH%
     - if "%configuration%" EQU "Debug" set DEBUG=1
     # uncomment lines below to update packages to use latest gcc
     #- bash -lc "pacman --noconfirm -Syuu"
     #- bash -lc "pacman --noconfirm -Syuu"
     #- if "%platform%" EQU "i686" bash -lc "pacman --noconfirm -S mingw-w64-i686-gcc mingw-w64-i686-make"
     #- if "%platform%" EQU "x86_64" bash -lc "pacman --noconfirm -S mingw-w64-x86_64-gcc mingw-w64-x86_64-make"
-    - if "%platform%" EQU "i686" set PATH=C:\msys64\mingw32\bin;%PATH:C:\Program Files\Git\usr\bin;=%
-    - if "%platform%" EQU "x86_64" set PATH=C:\msys64\mingw64\bin;%PATH:C:\Program Files\Git\usr\bin;=%
+    - ps: |
+        Write-Output "Tools version:"
+        Write-Output (((gcc --version) | select-object -first 1) + " " + (gcc -dumpmachine))
+        Write-Output (mingw32-make --version) | select-object -first 1
+        Write-Output (sh --version) | select-object -first 1
+        Write-Output ""
   build_script:
-    - mingw32-make -f PowerEditor\gcc\makefile
+    - make -f PowerEditor\gcc\makefile
   after_build:
     # artifacts
     - ps: |