Moved CFLAGS to root Makefile.

Makefile

@@ -1,4 +1,5 @@
 BUILD=build/
+CFLAGS := -g -O3 -pipe -Wall -Wextra -fstrict-aliasing
 
 # Fix pdflatex search path
 TEXINPUTS := "$(TEXINPUTS):docs"

external/rules.mk

@@ -5,13 +5,13 @@ PYBISON_INC := -Iexternal/pybison/src/c -I/usr/include/python2.7
 build: $(b)pybison/bison_.so $(b)pybison/bison.py
 
 $(b)pybison/bison_.so: $(b)pybison/bison_.o $(b)pybison/bisondynlib-linux.o
-	$(CC) -g -O3 -pipe -Wall -Wextra -shared -pthread -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) -g -O3 -pipe -Wall -Wextra -o $@ -c $< -pthread -fPIC $(PYBISON_INC)
+	$(CC) $(CFLAGS) -o $@ -c $< -pthread -fPIC $(PYBISON_INC)
 
 $(b)pybison/bisondynlib-linux.o: $(d)pybison/src/c/bisondynlib-linux.c
 $(b)pybison/bison_.o: $(b)pybison/bison_.c