Reorganise CLFAGS/LDFLAGS handling

Makefile

@@ -8,8 +8,17 @@ ifneq ($(wildcard ./.git/.),)
 VERSION := $(shell git describe --tags)
 endif
 
-CFLAGS += -I.
-LDFLAGS += -L.
+LIBS := $(shell pkg-config --libs   ${pkg_config_packs})
+INCS := $(shell pkg-config --cflags ${pkg_config_packs})
+
+ifneq (clean, $(MAKECMDGOALS))
+ifeq ($(and $(INCS),$(LIBS)),)
+$(error "pkg-config failed!")
+endif
+endif
+
+CFLAGS += -I. ${INCS}
+LDFLAGS+= -L. ${LIBS}
 
 SRC := $(sort $(shell find src/ -name '*.c'))
 OBJ := ${SRC:.c=.o}

config.mk

@@ -2,23 +2,24 @@
 PREFIX ?= /usr/local
 MANPREFIX = ${PREFIX}/share/man
 
-# Warning: This is deprecated behavior
 # uncomment to disable parsing of dunstrc
 # or use "CFLAGS=-DSTATIC_CONFIG make" to build
-#STATIC= -DSTATIC_CONFIG
-
-PKG_CONFIG:=$(shell which pkg-config)
-ifeq (${PKG_CONFIG}, ${EMPTY})
-$(error "Failed to find pkg-config, please make sure it is installed")
-endif
+#STATIC= -DSTATIC_CONFIG # Warning: This is deprecated behavior
 
 # flags
 CPPFLAGS += -D_DEFAULT_SOURCE -DVERSION=\"${VERSION}\"
 CFLAGS   += -g --std=gnu99 -pedantic -Wall -Wno-overlength-strings -Os ${STATIC} ${CPPFLAGS}
+LDFLAGS  += -lm -L${X11LIB}
 
-pkg_config_packs := dbus-1 x11 xscrnsaver \
-                    "glib-2.0 >= 2.36" gio-2.0 \
-                    pangocairo gdk-3.0 xrandr xinerama
+pkg_config_packs := dbus-1 \
+                    gio-2.0 \
+                    gdk-3.0 \
+                    "glib-2.0 >= 2.36" \
+                    pangocairo \
+                    x11 \
+                    xinerama \
+                    xrandr \
+                    xscrnsaver
 
 # check if we need libxdg-basedir
 ifeq (,$(findstring STATIC_CONFIG,$(CFLAGS)))
@@ -31,15 +32,3 @@ endif
 ifneq (,$(findstring dunstify,${MAKECMDGOALS}))
 	pkg_config_packs += libnotify
 endif
-
-# includes and libs
-INCS := $(shell ${PKG_CONFIG} --cflags ${pkg_config_packs})
-CFLAGS += ${INCS}
-LDFLAGS += -lm -L${X11LIB} -lXss $(shell ${PKG_CONFIG} --libs ${pkg_config_packs})
-
-# only make this an fatal error when where not cleaning
-ifneq (clean, $(MAKECMDGOALS))
-ifeq (${INCS}, ${EMPTY})
-$(error "pkg-config failed, see errors above")
-endif
-endif