Ignoring unused functions warnings.

This is achieved by adding the -Wno-unused-function flag to the compiler.
The warnings are suppressed to avoid confusion for users new to dwm.

Removing the static declaration from the header files works too, but adds
unnecessary data into the compiled object.

config.mk

@@ -58,7 +58,7 @@ LIBS = -L${X11LIB} -lX11 ${XINERAMALIBS} ${FREETYPELIBS}  ${XRENDER} ${MPDCLIENT
 # flags
 CPPFLAGS = -D_DEFAULT_SOURCE -D_BSD_SOURCE -D_POSIX_C_SOURCE=200809L -DVERSION=\"${VERSION}\" ${XINERAMAFLAGS}
 #CFLAGS   = -g -std=c99 -pedantic -Wall -O0 ${INCS} ${CPPFLAGS}
-CFLAGS   = -std=c99 -pedantic -Wall -Wno-deprecated-declarations -Os ${INCS} ${CPPFLAGS}
+CFLAGS   = -std=c99 -pedantic -Wall -Wno-unused-function -Wno-deprecated-declarations -Os ${INCS} ${CPPFLAGS}
 LDFLAGS  = ${LIBS}
 
 # Solaris