Fix _PI (define it for pass 2)

src/asm/symbol.c

@@ -751,6 +751,8 @@ sym_PrepPass2(void)
 	sym_AddEqu("_NARG", 0);
 	p_NARGSymbol = findsymbol("_NARG", NULL);
 	p_NARGSymbol->Callback = Callback_NARG;
+	
+	math_DefinePI();
 }
 
 /*