Makefile: fix linking and enable -Wall

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/Makefile b/Makefile
index a55897f..9d1f5b9 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
-CPPFLAGS=$(shell pkg-config --cflags libsystemd)
-LDFLAGS=$(shell pkg-config --libs libsystemd)
+CFLAGS	= $(shell pkg-config --cflags libsystemd) -Wall -O2
+LDLIBS	= $(shell pkg-config --libs libsystemd)
 
 EXE = btbridged