boru on Freenode's #gcc channel pointed out that
contrib/download_prerequisites should use shasum for FreeBSD, not
sha512sum (which comes from GNU coreutils on GNU/Linux). I checked
FreeBSD 11.0 and 10.2 and neither has sha512sum, not does DragonFly
4.2, another FreeBSD derivative.
OK for trunk?
diff --git a/contrib/download_prerequisites b/contrib/download_prerequisites
index ae0b5ffeb32..b50f47cda79 100755
--- a/contrib/download_prerequisites
+++ b/contrib/download_prerequisites
@@ -47,7 +47,7 @@ force=0
OS=$(uname)
case $OS in
- "Darwin")
+ "Darwin"|"FreeBSD"|"DragonFly")
chksum='shasum -a 512 --check'
;;
*)
