Stmt: Deprecate STMT_ANY

This isn't used in-tree and has been misused by some external plugins
of mine (zeekjs and zeek-perf-support) for their own Stmt subclasses.
These plugins should be updated to use the new STMT_EXTERN statement.

Handle STMT_ANY explicitly in stmt_name() for the time being
to fix #3529 until we remove STMT_ANY for good.

src/Stmt.cc

@@ -55,6 +55,12 @@ const char* stmt_name(StmtTag t) {
         "extern",
     };
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+    if ( int(t) == STMT_ANY )
+        return "any";
+#pragma GCC diagnostic pop
+
     return stmt_names[int(t)];
 }