[build] Look for isolinux.bin in more places

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Marty Connor <mdc@etherboot.org>

src/arch/i386/Makefile

 
 # Locations of utilities
 #
-ISOLINUX_BIN	= /usr/lib/syslinux/isolinux.bin
+ISOLINUX_BIN_LIST	:= \
+	$(ISOLINUX_BIN) \
+	/usr/lib/syslinux/isolinux.bin \
+	/usr/share/syslinux/isolinux.bin
+ISOLINUX_BIN	= $(firstword $(wildcard $(ISOLINUX_BIN_LIST)))
 
 # i386-specific directories containing source files
 #