Fix Makefile clean target of src/crangler

This target was previously not cleaning up the generated source file for
the lexer or the build binary. This issue was seen on Ubuntu and
resulted in cmake errors when using `make clean` as part of switching
from using the make build to using the cmake build.

Author: thomasspriggs

src/crangler/Makefile

@@ -17,7 +17,9 @@ INCLUDES= -I ..
 include ../config.inc
 include ../../$(CPROVER_DIR)/src/common
 
-CLEANFILES = crangler$(LIBEXT)
+CLEANFILES = crangler$(LIBEXT) \
+  c_lex.yy.cpp \
+  crangler$(EXEEXT)
 
 all: crangler$(EXEEXT)