Makefile: add Freebsd cflags/ldflags

Makefile

@@ -1,10 +1,22 @@
 CFILES=xcwd.c
 CC=gcc
-CFLAGS=-Wall -Werror -Wextra -pedantic -std=gnu99 -O2
+CFLAGS=-Wall -Werror -Wextra -std=gnu99 -O2
 LDFLAGS=-lX11
 EXE="xcwd"
-O=${CFILES:.c=.o}
 prefix=/usr/
+UNAME:=$(shell uname)
+O=${CFILES:.c=.o}
+
+ifeq ($(UNAME), Linux)
+    CFLAGS += -DLINUX
+else
+    ifeq ($(UNAME), FreeBSD)
+        CFLAGS += -I/usr/local/include/ -DFREEBSD
+        LDFLAGS += -L/usr/local/lib -lprocstat
+    else
+        $(error Operating System not supported.)
+    endif
+endif
 
 ${EXE}: clean ${O}
 	${CC} -o $@ ${O} ${CFLAGS} ${LDFLAGS}