Add support for Java interface method calls.
* cp-tree.h (struct lang_type): Add java_interface flag.
(TYPE_JAVA_INTERFACE): New macro.
* tree.c (cp_valid_lang_attribute): Handle "java_interface" attribute
by setting TYPE_JAVA_INTERFACE.
* call.c (java_iface_lookup_fn): New static.
(build_over_call): If calling a method declared in a
TYPE_JAVA_INTERFACE, call build_java_interface_fn_ref to generate the
expression which resolves the function address.
(build_java_interface_fn_ref): New function.