meta-digi-arm: fix build error in imx-bootlets-dey

With yocto 1.8 we need to pass CC and LD from yocto environment to
imx-bootlets makefile. Otherwise it fails:

arm-dey-linux-gnueabi-ld: cannot find -lgcc
make[1]: *** [output-target/linux_prep] Error 1

https://jira.digi.com/browse/DEL-1558

Signed-off-by: Javier Viguera <javier.viguera@digi.com>

meta-digi-arm/recipes-bsp/imx-bootlets-dey/imx-bootlets-dey_git.bb

@@ -20,7 +20,12 @@ S = "${WORKDIR}/git"
 # Disable parallel building or it may fail to build.
 PARALLEL_MAKE = ""
 
-EXTRA_OEMAKE = "CROSS_COMPILE=${TARGET_PREFIX} BOARD=${IMXBOOTLETS_MACHINE}"
+EXTRA_OEMAKE = "\
+    BOARD='${IMXBOOTLETS_MACHINE}' \
+    CROSS_COMPILE='${TARGET_PREFIX}' \
+    CC='${CC}' \
+    LD='${LD}' \
+"
 
 # Ensure machine defines the IMXBOOTLETS_MACHINE
 python () {