Skylark: Make ctx.var a dictionary.

ctx.var(x) is kept for compatibility and should be removed after next
release.

--
MOS_MIGRATED_REVID=88438195
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Package.java b/src/main/java/com/google/devtools/build/lib/packages/Package.java
index 900f901..5d2bafd 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Package.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Package.java
@@ -452,6 +452,17 @@
   }
 
   /**
+   * Returns all make variables for a given platform.
+   */
+  public Map<String, String> getAllMakeVariables(String platform) {
+    ImmutableMap.Builder<String, String> map = ImmutableMap.builder();
+    for (String var : makeEnv.getBindings().keySet()) {
+      map.put(var, makeEnv.lookup(var, platform));
+    }
+    return map.build();
+  }
+
+  /**
    * Returns the label of this package's BUILD file.
    *
    * Typically <code>getBuildFileLabel().getName().equals("BUILD")</code> --