Instead of overriding, append flags

Author: AMDmi3

Makefile

@@ -1,7 +1,7 @@
-CFLAGS = $(shell pkg-config --cflags freetype2 x11 openal)
+CFLAGS += $(shell pkg-config --cflags freetype2 x11 openal)
 CFLAGS += $(shell pkg-config --cflags dbus-1)
 CFLAGS += -g -pthread -std=gnu99
-LDFLAGS = $(shell pkg-config --libs freetype2 x11 openal)
+LDFLAGS += $(shell pkg-config --libs freetype2 x11 openal)
 LDFLAGS += $(shell pkg-config --libs dbus-1)
 LDFLAGS += -lX11 -lXft -lXrender -ltoxcore -ltoxav -ltoxdns -lopenal -pthread -lresolv -ldl -lm -lfontconfig -lv4lconvert -lvpx -lXext