armv7-m/irq: fix the greenhills compiler compile error

CXX:  libcxxmini/libxx_new.cxx "/home/guoshichao/work_profile/vela_os/vela_qemu_1/nuttx/include/arch/armv7-m/irq.h", line 594: error apache#3422:
          use of the "register" storage class specifier is not allowed
    register uint32_t sp;
    ^

"/home/guoshichao/work_profile/vela_os/vela_qemu_1/nuttx/include/arch/armv7-m/irq.h", line 594: error apache#3422:
          use of the "register" storage class specifier is not allowed
    register uint32_t sp;
    ^

"/home/guoshichao/work_profile/vela_os/vela_qemu_1/nuttx/include/arch/armv7-m/irq.h", line 594: error apache#3422:
          use of the "register" storage class specifier is not allowed
    register uint32_t sp;
    ^

make[1]: *** [Makefile:69: libxx_delete_sized.o] Error 1
make[1]: *** Waiting for unfinished jobs....
make[1]: *** [Makefile:69: libxx_deletea_sized.o] Error 1
make[1]: *** [Makefile:69: libxx_new.o] Error 1
"/home/guoshichao/work_profile/vela_os/vela_qemu_1/nuttx/include/arch/armv7-m/irq.h", line 594: error apache#3422:
          use of the "register" storage class specifier is not allowed
    register uint32_t sp;
    ^

"/home/guoshichao/work_profile/vela_os/vela_qemu_1/nuttx/include/arch/armv7-m/irq.h", line 594: error apache#3422:
          use of the "register" storage class specifier is not allowed
    register uint32_t sp;
    ^

Signed-off-by: guoshichao <[email protected]>

Author: extinguish

include/nuttx/compiler.h

@@ -82,6 +82,7 @@
 #if defined(__ghs__)
 
 #  define __extension__
+#  define register
 
 #endif