Use the in-tree sys/elf_common.h

This is the same fix as r301471.

usr.bin/elfcopy/Makefile

@@ -30,4 +30,17 @@ MAN=	${PROG}.1 strip.1
 
 LINKS=	${BINDIR}/${PROG} ${BINDIR}/strip
 
+# This same hack is in lib/libelf/Makefile and usr.bin/readelf/Makefile
+# We need to link against the correct version of these files. One
+# solution is to include ../../sys in the include path. This causes
+# problems when a header file in sys depends on a file in another
+# part of the tree, e.g. a machine dependent header.
+#
+SRCS+=		sys/elf_common.h
+CLEANDIRS=	sys
+CFLAGS+=	-I.
+sys/elf_common.h: ${SRCTOP}/sys/${.TARGET} .NOMETA
+	mkdir -p ${.OBJDIR}/sys
+	ln -sf ${.ALLSRC} ${.TARGET}
+
 .include <bsd.prog.mk>