Fix windres failing when building from another directory

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@3361

src/Makefile.am

@@ -5,16 +5,16 @@ SUBDIRS = cpu debug dos fpu gui hardware libs ints misc shell platform
 bin_PROGRAMS = dosbox
 
 if HAVE_WINDRES
-ico_stuff = dosbox_ico.o
+ico_stuff = winres.rc
 endif
 
+.rc.o:
+	$(WINDRES) -o $@ $<
 
-dosbox_SOURCES = dosbox.cpp
+dosbox_SOURCES = dosbox.cpp $(icostuff)
 dosbox_LDADD = cpu/libcpu.a debug/libdebug.a dos/libdos.a fpu/libfpu.a  hardware/libhardware.a gui/libgui.a \
-               ints/libints.a misc/libmisc.a shell/libshell.a hardware/serialport/libserial.a libs/gui_tk/libgui_tk.a\
-	       $(ico_stuff)
+               ints/libints.a misc/libmisc.a shell/libshell.a hardware/serialport/libserial.a libs/gui_tk/libgui_tk.a
+
+EXTRA_DIST = winres.rc dosbox.ico
 
-EXTRA_DIST = dosbox.rc dosbox.ico
-dosbox_ico.o: dosbox.rc dosbox.ico
-	$(WINDRES) dosbox.rc dosbox_ico.o