Simplify MSYS2 scripts

Win/Scripts/msys2-mingw64-gcc-x64-msvcrt-libstdc++.bat

@@ -1,3 +0,0 @@
-@echo off
-setlocal EnableDelayedExpansion
-%devenver_root%\msys2\20240113\msys2_shell.cmd -defterm -here -use-full-path -no-start -mingw64 -shell bash

Win/Scripts/msys2-msys-gcc-x64-cygwin-libstdc++.bat

@@ -1,3 +0,0 @@
-@echo off
-setlocal EnableDelayedExpansion
-%devenver_root%\msys2\20240113\msys2_shell.cmd -defterm -here -use-full-path -no-start -msys -shell bash

Win/Scripts/msys2-ucrt64-gcc-x64-ucrt-libstdc++.bat

@@ -1,3 +0,0 @@
-@echo off
-setlocal EnableDelayedExpansion
-%devenver_root%\msys2\20240113\msys2_shell.cmd -defterm -here -use-full-path -no-start -ucrt64 -shell bash

Win/Scripts/msys2_env.bat

@@ -0,0 +1,27 @@
+@echo off
+setlocal EnableDelayedExpansion
+
+if "%~1"=="help"   goto :help
+if "%~1"==""       goto :help
+if "%~1"=="--help" goto :help
+if "%~1"=="/?"     goto :help
+if "%~2"==""       goto :help
+goto :run
+
+:help
+echo USAGE: msys2_env.bat ^<environment^> ^<command^>
+echo.
+echo ENVIRONMENTS:
+echo   ^| Name      ^| Toolchain ^| Arch ^| C Runtime ^| C++ Runtime ^|
+echo   ^| 'clang64' ^| llvm      ^| x64  ^| ucrt      ^| libc++      ^|
+echo   ^| 'mingw32' ^| gcc       ^| x86  ^| msvcrt    ^| libstdc++   ^|
+echo   ^| 'mingw64' ^| gcc       ^| x64  ^| msvcrt    ^| libstdc++   ^|
+echo   ^| 'msys2'   ^| gcc       ^| x64  ^| cygwin    ^| libstdc++   ^|
+echo   ^| 'ucrt64'  ^| gcc       ^| x64  ^| ucrt      ^| libstdc++   ^|
+goto :eof
+
+:run
+set msys_env=%~1
+for /f "tokens=1,* delims= " %%a in ("%*") do set remaining_args=%%b
+
+%devenver_root%\MSYS2\20240113\msys2_shell.cmd -%msys_env% -no-start -defterm -here -c "%remaining_args%"