Move config.mk into Makefile, and delete config.mk.

config.mk shall now contain user-specific configurations, and thus is
now ignored.

Makefile

@@ -1,12 +1,30 @@
 # dwm - dynamic window manager
 # See LICENSE file for copyright and license details.
 
-include config.mk
+-include config.mk
+
+VERSION = 6.7
 
 INSTALL ?= install
 GZIP    ?= gzip
 TAR     ?= tar
 
+CFLAGS   := -Os $(CFLAGS) -g -std=gnu99\
+	    -Wall -Wextra -Wpedantic -Wno-pointer-arith
+CPPFLAGS := -DNDEBUG $(CPPFLAGS)\
+	    -DVERSION=\"$(VERSION)\" -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=700L -DXINERAMA
+LDFLAGS  := -flto $(LDFLAGS)
+LDLIBS   := $(LDLIBS) -lm
+
+# Use pkg-config to locate dependencies, and set the correct flags.
+ifeq (,$(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 x11 xinerama)
+LDFLAGS  += $(shell pkg-config --libs-only-L   x11 xinerama)
+LDLIBS   += $(shell pkg-config --libs-only-l   x11 xinerama)
+endif
+
 SRC := $(wildcard src/*.c)
 OBJ := $(addsuffix .o,$(SRC))
 DEP := $(addsuffix .d,$(SRC))