Add a const version of gdb_argv:as_array_view

This commits adds const versions for the GET and AS_ARRAX_VIEW methods
of gdb_argv.  Those methods will be required in the following patch of
the series.

gdb/utils.h

diff --git a/gdb/utils.h b/gdb/utils.h
index f05e662..6f3a702 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -195,6 +195,11 @@ class gdb_argv
     return m_argv;
   }
 
+  const char * const * get () const
+  {
+    return m_argv;
+  }
+
   /* Return the underlying array, transferring ownership to the
      caller.  */
 
@@ -227,6 +232,11 @@ class gdb_argv
     return gdb::array_view<char *> (this->get (), this->count ());
   }
 
+  gdb::array_view<const char * const> as_array_view () const
+  {
+    return gdb::array_view<const char * const> (this->get (), this->count ());
+  }
+
   /* Append arguments to this array.  */
   void append (gdb_argv &&other)
   {