zoul: only run date once per compilation
There is a single file that needs date,
so stop running date on every compiler
invocation.
@@ -19,7 +19,8 @@ BSL_FLAGS += -e -w -v
BSL_SPEED ?= 460800
# Works in Linux and probably on OSX too (RTCC example)
-CFLAGS += -DDATE="\"`date +"%02u %02d %02m %02y %02H %02M %02S"`\""
+COMPILE_DATE := $(shell date +"%02u %02d %02m %02y %02H %02M %02S")
+CFLAGS += -DDATE="\"$(COMPILE_DATE)\""
### Configure the build for the board and pull in board-specific sources
CONTIKI_TARGET_DIRS += . dev
