Pin build<1.4.3 to work around PYTHONPATH stripping regression

build 1.4.3 (pypa/build#1024) strips PYTHONPATH from isolated build
subprocesses but not from the pip install step that populates them.
When install_hostpython_prerequisites puts packages (including
setuptools) on PYTHONPATH via --target, pip sees setuptools as
"already satisfied" and skips installing it into the isolated venv.
The build backend subprocess then fails with:
  BackendUnavailable: Cannot import 'setuptools.build_meta'

See pypa/build#1037.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: rtibbles

pythonforandroid/recipe.py

@@ -1266,7 +1266,7 @@ def install_wheel(self, arch, built_wheels):
 
     def build_arch(self, arch):
         self.install_hostpython_prerequisites(
-            packages=["build[virtualenv]", "pip"] + self.hostpython_prerequisites
+            packages=["build[virtualenv]<1.4.3", "pip"] + self.hostpython_prerequisites
         )
         build_dir = self.get_build_dir(arch.arch)
         env = self.get_recipe_env(arch, with_flags_in_cc=True)