buildgcc: improve portability

`cp --remove-destination` isn't as portable as `rm -f` and `cp`.

Change-Id: Ib05bfc121f7a0b467f8104920e14fbd02191585f
Signed-off-by: Jonathan A. Kollasch <jakllsch@kollasch.net>
Reviewed-on: http://review.coreboot.org/150
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
diff --git a/util/crossgcc/buildgcc b/util/crossgcc/buildgcc
index e97a651..e58b23e 100755
--- a/util/crossgcc/buildgcc
+++ b/util/crossgcc/buildgcc
@@ -463,7 +463,8 @@
 	rm -f .failed
 	CFLAGS="$HOSTCFLAGS"
 	$MAKE || touch .failed
-	cp --remove-destination iasl* $DESTDIR$TARGETDIR/bin || touch .failed
+	rm -f $DESTDIR$TARGETDIR/bin/iasl || touch .failed
+	cp iasl $DESTDIR$TARGETDIR/bin || touch .failed
 	if [ ! -f .failed ]; then touch .success; fi
 ) &> $IASL_DIR/compiler/crossgcc-build.log
 test -r $IASL_DIR/compiler/.failed && printf "${RED}failed${NC}\n" || printf "${green}ok${NC}\n"