__CCRX__ only applyes to version 4 of RX family compiler http://tool-support.renesas.com/autoupdate/support/onlinehelp/csp/V4.01.00/CS+.chm/Compiler-CCRX.chm/Output/ccrx04c0201y.html __RX__ is one of the macros exported by latest gcc (gcc_8.3.0.202305_rx_elf)