sencha: use xmake -b instead of xmake build

"-b" is almost equivalent to "build"; it also supports specifying targets.
Use it instead to simplify doing c&p from the build log.

Change-Id: Iabc32d53622e434bfcea6b71698f63cbbfd4091b

platforms/sencha/cheriot.mk

diff --git a/platforms/sencha/cheriot.mk b/platforms/sencha/cheriot.mk
index 8481826..0e5e4d4 100644
--- a/platforms/sencha/cheriot.mk
+++ b/platforms/sencha/cheriot.mk
@@ -117,7 +117,7 @@
 			--sdk=${ROOTDIR}/cache/cheriot-tools \
 			--board=${CHERIOT_BOARD} \
 			${CHERIOT_DEBUG_CONFIG_OPTIONS} && \
-	xmake build
+	xmake -b
 
 ## Generates CHERIoT build artifacts with debugging suport
 cheriot-bundle-debug: $(CHERIOT_FIRMWARE_DEBUG)
@@ -130,7 +130,7 @@
 			--sdk=${ROOTDIR}/cache/cheriot-tools \
 			--board=${CHERIOT_BOARD} \
 			${CHERIOT_RELEASE_CONFIG_OPTIONS} && \
-	xmake build
+	xmake -b
 
 ## Generates CHERIoT build artifacts setup for release
 cheriot-bundle-release: $(CHERIOT_FIRMWARE_RELEASE)