iiod/serial.c: fix sparc build

Fix the following sparc build failure raised since version 0.24 and
2d3cae0:

/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c: In function 'serial_configure':
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:99:58: error: 'B2500000' undeclared (first use in this function); did you mean 'B1500000'?
   99 | #define CASE_BPS(bps, attr) case bps: (attr)->c_cflag |= B##bps; break
      |                                                          ^
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:127:9: note: in expansion of macro 'CASE_BPS'
  127 |         CASE_BPS(2500000, &tty_attrs);
      |         ^~~~~~~~
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:99:58: note: each undeclared identifier is reported only once for each function it appears in
   99 | #define CASE_BPS(bps, attr) case bps: (attr)->c_cflag |= B##bps; break
      |                                                          ^
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:127:9: note: in expansion of macro 'CASE_BPS'
  127 |         CASE_BPS(2500000, &tty_attrs);
      |         ^~~~~~~~
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:99:58: error: 'B3000000' undeclared (first use in this function); did you mean 'B1000000'?
   99 | #define CASE_BPS(bps, attr) case bps: (attr)->c_cflag |= B##bps; break
      |                                                          ^
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:128:9: note: in expansion of macro 'CASE_BPS'
  128 |         CASE_BPS(3000000, &tty_attrs);
      |         ^~~~~~~~
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:99:58: error: 'B3500000' undeclared (first use in this function); did you mean 'B1500000'?
   99 | #define CASE_BPS(bps, attr) case bps: (attr)->c_cflag |= B##bps; break
      |                                                          ^
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:129:9: note: in expansion of macro 'CASE_BPS'
  129 |         CASE_BPS(3500000, &tty_attrs);
      |         ^~~~~~~~
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:99:58: error: 'B4000000' undeclared (first use in this function); did you mean 'B1000000'?
   99 | #define CASE_BPS(bps, attr) case bps: (attr)->c_cflag |= B##bps; break
      |                                                          ^
/home/buildroot/autobuild/instance-0/output-1/build/libiio-0.24/iiod/serial.c:130:9: note: in expansion of macro 'CASE_BPS'
  130 |         CASE_BPS(4000000, &tty_attrs);
      |         ^~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/8a9902f6eddaab812ebce3506ed6de686f647e02

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

iiod/serial.c

@@ -124,10 +124,18 @@ static int serial_configure(int fd, unsigned int uart_bps,
 	CASE_BPS(1152000, &tty_attrs);
 	CASE_BPS(1500000, &tty_attrs);
 	CASE_BPS(2000000, &tty_attrs);
+#ifdef B2500000 /* Not available on all architectures, i.e. sparc */
 	CASE_BPS(2500000, &tty_attrs);
+#endif
+#ifdef B3000000 /* Not available on all architectures, i.e. sparc */
 	CASE_BPS(3000000, &tty_attrs);
+#endif
+#ifdef B3500000 /* Not available on all architectures, i.e. sparc */
 	CASE_BPS(3500000, &tty_attrs);
+#endif
+#ifdef B4000000 /* Not available on all architectures, i.e. sparc */
 	CASE_BPS(4000000, &tty_attrs);
+#endif
 	default:
 		IIO_ERROR("Invalid baud rate\n");
 		return -EINVAL;