Auto merge of #288 - fitzgen:allow-custom-bindgen-path, r=Ms2ger

Allow a custom path to bindgen in etc/bindings.sh

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Author: bors-servo

etc/bindings.sh

@@ -10,7 +10,15 @@ if [[ "$1" == "msvc14" ]] ; then
     EXTRA_FLAGS="$EXTRA_FLAGS -fvisibility=hidden"
 fi
 
-../../rust-bindgen/target/debug/bindgen \
+: ${BINDGEN:=../../rust-bindgen/target/debug/bindgen}
+
+if [[ ! -x "$BINDGEN" ]]; then
+    echo "error: BINDGEN does not exist or isn't executable!"
+    echo "error: with BINDGEN=$BINDGEN"
+    exit 1
+fi
+
+$BINDGEN \
   ${EXTRA_FLAGS} \
   -no-class-constants \
   -no-type-renaming \