Change sdk/bin/dart2js to find an available build.

sdk/bin/dart2js

 #!/usr/bin/env bash
 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 function follow_links() {
   file="$1"
   while [ -h "$file" ]; do
     # On Mac OS, readlink -f doesn't work.
     file="$(readlink "$file")"
@@ skipping 34 matching lines @@
 # We allow extra vm options to be passed in through an environment variable.
 if [[ $DART_VM_OPTIONS ]]; then
   read -a OPTIONS <<< "$DART_VM_OPTIONS"
   EXTRA_VM_OPTIONS+=("${OPTIONS[@]}")
 fi
 
 DART_ROOT="$(cd "${SDK_DIR}/.." ; pwd -P)"
 
 DART2JS="$DART_ROOT/pkg/compiler/lib/src/dart2js.dart"
 
+if [[ `uname` == 'Darwin' ]]; then
+  OUT_DIR="$DART_ROOT/xcodebuild/"
+else
+  OUT_DIR="$DART_ROOT/out/"
+fi
+
 if [ -z "$DART_CONFIGURATION" ];
 then
-  DART_CONFIGURATION="ReleaseX64"
+  DIRS=$( ls "$OUT_DIR" )
+  # list of possible configurations in decreasing desirability
+  CONFIGS=("ReleaseX64" "ReleaseIA32" "DebugX64" "DebugIA32"
+    "ReleaseARM"    "ReleaseARM64"    "ReleaseARMV5TE"    "ReleaseMIPS"
+    "DebugARM"      "DebugARM64"      "DebugARMV5TE"      "DebugMIPS")
+  DART_CONFIGURATION="None"
+  for CONFIG in ${CONFIGS[*]}
+  do
+    for DIR in $DIRS;
+    do
+      if [ "$CONFIG" = "$DIR" ];
+      then
+        # choose most desirable configuration that is available and break
+        DART_CONFIGURATION="$DIR"
+        break 2
+      fi
+    done
+  done
+  if [ "$DART_CONFIGURATION" = "None" ]
+  then
+    echo "No valid dart configuration found in $OUT_DIR"
+    exit 1
+  fi
 fi
 
-if [[ `uname` == 'Darwin' ]]; then
-  BUILD_DIR="$DART_ROOT/xcodebuild/$DART_CONFIGURATION"
-else
-  BUILD_DIR="$DART_ROOT/out/$DART_CONFIGURATION"
-fi
+BUILD_DIR="$OUT_DIR$DART_CONFIGURATION"
 
 PACKAGE_ROOT="$BUILD_DIR/packages/"
 
 exec "$DART" "${EXTRA_VM_OPTIONS[@]}" "--package-root=$PACKAGE_ROOT" "$DART2JS" "${EXTRA_OPTIONS[@]}" "$@"