make: Improvements to a couple of makefiles

- Depend.mk, ldlibpath.mk:
  add multiple inclusion guards
- Flex-bison.mk
  some dependency fiddling
- Py-defs.mk:
  remove *.pyc on clean

Signed-off-by: Jan Lindemann <jan@janware.com>

make/py-defs.mk

@@ -36,6 +36,8 @@ PYTHONPATH           ?= $(call proj_query, pythonpath $(PROJECT))
 export PYTHONPATH
 
 all:
+clean: pyc.clean
+
 echo-py:
 	@echo PROJECT = $(PROJECT)
 	@echo PY_PROJ_MODULE_DIRS = $(PY_PROJ_MODULE_DIRS)
@@ -46,6 +48,8 @@ echo-py:
 	@echo PY_INSTALL_MOD = $(PY_INSTALL_MOD)
 	@echo PY_INSTALL_SUB_MOD = $(PY_INSTALL_SUB_MOD)
 
+pyc.clean:
+	rm -f $(wildcard *.pyc)
 libpath: py-libpath
 py-libpath:
 	@echo export PYTHONPATH=$(PYTHONPATH)