libcc1: use GCC_FE_VERSION_1 in C++ plugin

The C++ plugin defaults to version 0 of the base compiler API.
However, this is a mistake -- version 1 was introduced before the C++
API was even implemented.  This switches the default to version 1.
Note that the compiler-side plugin will accept this version, so it
should remain compatible.

libcc1

	* libcp1.cc (vtable): Use GCC_FE_VERSION_1.

libcc1/libcp1.cc

@@ -391,7 +391,7 @@ libcp1_destroy (struct gcc_base_context *s)
 
 static const struct gcc_base_vtable vtable =
 {
-  GCC_FE_VERSION_0,
+  GCC_FE_VERSION_1,
   libcp1_set_arguments_v0,
   libcp1_set_source_file,
   libcp1_set_print_callback,