Do not create a symbolic link to bison.py.

external/rules.mk

@@ -2,14 +2,11 @@ TGT_DIR += $(b)pybison
 
 PYBISON_INC := -Iexternal/pybison/src/c -I/usr/include/python2.7
 
-build: $(b)pybison/bison_.so $(b)pybison/bison.py
+build: $(b)pybison/bison_.so
 
 $(b)pybison/bison_.so: $(b)pybison/bison_.o $(b)pybison/bisondynlib-linux.o
 	$(CC) $(CFLAGS) -shared -pthread -o $@ $^
 
-$(b)pybison/bison.py: $(d)pybison/src/python/bison.py | $(b)pybison
-	ln -s `realpath $<` $@
-
 $(b)pybison/bisondynlib-linux.o $(b)pybison/bison_.o: | $(b)pybison
 	$(CC) $(CFLAGS) -o $@ -c $< -pthread -fPIC $(PYBISON_INC)
 

tests/rules.mk

@@ -9,6 +9,8 @@ else
 COVERAGE=/usr/bin/coverage
 endif
 
+CLEAN := $(CLEAN) $(COVERAGE_OUTPUT_DIR)
+
 .PHONY: test coverage $(TESTS)
 
 test: $(TESTS) build