buildPython*: don't catch conflicts when cross-compiling

Hack until we fix PYTHONPATH.

pkgs/development/interpreters/python/mk-python-derivation.nix

@@ -53,7 +53,9 @@
 , disabled ? false
 
 # Raise an error if two packages are installed with the same name
-, catchConflicts ? true
+# TODO: For cross we probably need a different PYTHONPATH, or not
+# add the runtime deps until after buildPhase.
+, catchConflicts ? (python.stdenv.hostPlatform == python.stdenv.buildPlatform)
 
 # Additional arguments to pass to the makeWrapper function, which wraps
 # generated binaries.