genex/Makefile: add dependency generation (.d method)

Straight from fped/Makefile

genex/Makefile

@@ -9,9 +9,11 @@
 # (at your option) any later version.
 #
 
-CFLAGS = -Wall -g
 OBJS = genex.o comp.o libs.o pdf.o
 
+SHELL = /bin/bash
+CFLAGS = -Wall -g
+
 CC_normal	:= $(CC)
 DEPEND_normal	:= $(CPP) $(CFLAGS) -MM -MG
 
@@ -36,8 +38,18 @@ all:		genex
 genex:		$(OBJS)
 		$(CC) $(CFLAGS) -o $@ $(OBJS) $(LDLIBS)
 
+%.o:		%.c
+		$(CC) -c $(CFLAGS) $*.c -o $*.o
+		$(DEPEND) $*.c | \
+		  sed -e \
+		    '/^\(.*:\)\? */{p;s///;s/ *\\\?$$/ /;s/  */:\n/g;H;}' \
+		    -e '$${g;p;}' -e d >$*.d; \
+		  [ "$${PIPESTATUS[*]}" = "0 0" ] || { rm -f $*.d; exit 1; }
+
+-include $(OBJS:.o=.d)
+
 clean:
-		rm -f $(OBJS)
+		rm -f $(OBJS) $(OBJS:.o=.d)
 
 spotless:	clean
 		rm -f genex