Use native packages over included submodules.

This is the best option out of all, since it removes the requirement of
manually managing the dependencies, and should not matter for stable
ABI.

.gitmodules

@@ -1,7 +0,0 @@
-[submodule "lib/glfw"]
-	path = lib/glfw
-	url = https://github.com/glfw/glfw
-
-[submodule "lib/libarchive"]
-	path = lib/libarchive
-	url = https://github.com/libarchive/libarchive

Makefile

@@ -20,10 +20,19 @@ DEP := $(addsuffix .d,$(SRC))
 CFLAGS   := -O2 $(CFLAGS) -g -std=gnu99\
 	    -Wall -Wextra -Wpedantic -Wno-pointer-arith
 CPPFLAGS := -DNDEBUG $(CPPFLAGS) -DGLFW_INCLUDE_NONE\
-	    -Iinclude -Ilib/glad/include -Ilib/glfw/include -Ilib/libarchive/libarchive
+	    -Iinclude -Ilib/glad/include
-LDFLAGS  := -flto $(LDFLAGS)\
+LDFLAGS  := -flto $(LDFLAGS)
-	    -Llib/obj/glfw/src -Llib/obj/libarchive/libarchive
+LDLIBS   := $(LDLIBS) -lm
-LDLIBS   := $(LDLIBS) -lglfw3 -larchive -lm
+
+# Use pkg-config to locate dependencies, and set the correct flags.
+ifeq (,$(shell command -v pkg-config))
+$(error Failed to locate pkg-config, please make sure it is installed or acessible through PATH.)
+else
+CPPFLAGS += $(shell pkg-config --cflags-only-I glfw3 libarchive)
+LDFLAGS  += $(shell pkg-config --libs-only-L   glfw3 libarchive)
+LDLIBS   += $(shell pkg-config --libs-only-l   glfw3 libarchive)
+endif
+
 
 msg-cc    = $(info	[CC]	$(1))
 msg-clean = $(info	[CLEAN]	$(1))