fix msys build

forward port to get code in sync with 1.4-maint.

use "pip install -e ." before invoking pyinstaller, so we have
the _version.py built by setuptools_scm and also it compiled the
extension modules, so pyinstaller can pick them up.

msys2 hack:

https://stackoverflow.com/questions/76079590/error-plat-name-must-be-one-of-win32-win-amd64-win-arm32-win-arm6

.github/workflows/ci.yml

@@ -224,8 +224,11 @@ jobs:
         run: ./scripts/msys2-install-deps development
       - name: Build
         run: |
-          pip install -e .
+          # build borg.exe
+          SETUPTOOLS_USE_DISTUTILS=stdlib pip install -e .
           pyinstaller -y scripts/borg.exe.spec
+          # build sdist and wheel in dist/...
+          SETUPTOOLS_USE_DISTUTILS=stdlib python -m build
       - uses: actions/upload-artifact@v3
         with:
           name: borg-windows

scripts/msys2-install-deps

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-pacman -S --needed --noconfirm git mingw-w64-ucrt-x86_64-{toolchain,pkgconf,zstd,lz4,xxhash,openssl,python-msgpack,python-argon2_cffi,python-platformdirs,python,cython,python-setuptools,python-wheel,python-pkgconfig,python-packaging,python-pip}
+pacman -S --needed --noconfirm git mingw-w64-ucrt-x86_64-{toolchain,pkgconf,zstd,lz4,xxhash,openssl,python-msgpack,python-argon2_cffi,python-platformdirs,python,cython,python-setuptools,python-wheel,python-build,python-pkgconfig,python-packaging,python-pip}
 pip install pyinstaller
 
 if [ "$1" = "development" ]; then