Add mig tool to superenv

Necessary because it otherwise calls actual cc after it does whatever it does. So we force it to call our cc.

Library/ENV/4.3/mig

@@ -0,0 +1,3 @@
+#!/bin/bash
+pwd="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+exec xcrun mig -cc $pwd/cc "$@"

Library/ENV/4.3/xcrun

@@ -3,10 +3,17 @@
 # But many build-systems expect it to work. This fixes that.
 # NOTE only works if they call xcrun without a full-path. Cross your fingers!
 
+[ "$#" -eq 0 ] && exec /usr/bin/xcrun
+
 if [ $HOMEBREW_SDKROOT ]; then
   arg0="$1"
   shift
 
+  case $arg0 in
+  -*)
+    exec /usr/bin/xcrun "$arg0" "$@";;
+  esac
+
   path=$(/usr/bin/xcrun -find $arg0)
   [ -x "$path" ] && exec "$path" "$@"