python: add PYTHONPATH var; this allows packages to configure it

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

lang/python/files/python-package.mk

@@ -20,8 +20,9 @@ PYTHON:=python$(PYTHON_VERSION)
 HOST_PYTHON_LIB_DIR:=$(STAGING_DIR_HOST)/lib/python$(PYTHON_VERSION)
 HOST_PYTHON_BIN:=$(STAGING_DIR_HOST)/bin/python2
 
+PYTHONPATH:=$(PYTHON_LIB_DIR):$(STAGING_DIR)/$(PYTHON_PKG_DIR)
 define HostPython
-	(	export PYTHONPATH="$(PYTHON_LIB_DIR):$(STAGING_DIR)/$(PYTHON_PKG_DIR)"; \
+	(	export PYTHONPATH="$(PYTHONPATH)"; \
 		export PYTHONOPTIMIZE=""; \
 		export PYTHONDONTWRITEBYTECODE=1; \
 		$(1) \