Bug 702724 - Avoid compiler error when JDK version >= 7 [r=kats]

config/android-common.mk

@@ -66,6 +66,7 @@ endif
 
 JAVAC_FLAGS = \
   -target $(JAVA_VERSION) \
+  -source $(JAVA_VERSION) \
   -classpath $(JAVA_CLASSPATH) \
   -bootclasspath $(JAVA_BOOTCLASSPATH) \
   -encoding ascii \