remove _POSIX_C_SOURCE cflag

config.mk

@@ -17,9 +17,8 @@ INCS = -I${X11INC}
 LIBS = -L${X11LIB} -lX11 ${XINERAMALIBS}
 
 # flags
-CPPFLAGS = -D_BSD_SOURCE -D_POSIX_C_SOURCE=2 -DVERSION=\"${VERSION}\" ${XINERAMAFLAGS}
-#CFLAGS   = -g -std=c99 -pedantic -Wall -O0 ${INCS} ${CPPFLAGS}
-CFLAGS   = -std=c99 -pedantic -Wall -Os ${INCS} ${CPPFLAGS}
+CPPFLAGS = -D_BSD_SOURCE -DVERSION=\"${VERSION}\" ${XINERAMAFLAGS}
+CFLAGS   = -ansi -pedantic -Wall -Os ${INCS} ${CPPFLAGS}
 LDFLAGS  = -s ${LIBS}
 
 # compiler and linker