meta-toolchain-sdk: Use ?= when setting TOOLCHAIN_TARGET_TASK

git-svn-id: https://svn.o-hand.com/repos/poky/trunk@3855 311d38ba-8fff-0310-9ca6-ca027cbcb966

meta/packages/meta/meta-toolchain-sdk.bb

-TOOLCHAIN_TARGET_TASK = "task-poky-standalone-gmae-sdk-target task-poky-standalone-gmae-sdk-target-dbg"
+TOOLCHAIN_TARGET_TASK ?= "task-poky-standalone-gmae-sdk-target task-poky-standalone-gmae-sdk-target-dbg"
 TOOLCHAIN_OUTPUTNAME = "${SDK_NAME}-toolchain-sdk-${DISTRO_VERSION}"
 require meta-toolchain.bb