run.bash: fix freebsd build (i hope)

R=adg
CC=golang-dev
https://golang.org/cl/2012041
diff --git a/src/run.bash b/src/run.bash
index 4eb4a47..dc66202 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -6,6 +6,7 @@
 set -e
 . ./env.bash
 
+unset MAKEFLAGS  # single-threaded make
 unset CDPATH	# in case user has it set
 
 # no core files, please