target/semihosting: export semihosting_common_handlers[] from header file

Signed-off-by: Erhan Kurubas <erhan.kurubas@espressif.com>
Change-Id: I4add0c1dc7888497ee90fd02754607a16434b66f
Reviewed-on: https://review.openocd.org/c/openocd/+/7075
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/riscv/riscv.c

@@ -3114,7 +3114,6 @@ static const struct command_registration riscv_exec_command_handlers[] = {
  * protocol, then a command like `riscv semihosting enable` will make
  * sense, but for now all semihosting commands are prefixed with `arm`.
  */
-extern const struct command_registration semihosting_common_handlers[];
 
 const struct command_registration riscv_command_handlers[] = {
 	{