some architecture has no sub-arch like msp430, so
we should honor this because otherwise the configure-scripts
for binutils and gcc won't work the right way
TARGET_ARCH = "INVALID"
TARGET_OS = "INVALID"
TARGET_VENDOR = "${BUILD_VENDOR}"
-TARGET_SYS = "${TARGET_ARCH}${TARGET_VENDOR}-${TARGET_OS}"
+TARGET_SYS = "${TARGET_ARCH}${TARGET_VENDOR}${@['-' + bb.data.getVar('TARGET_OS', d, 1), ''][bb.data.getVar('TARGET_OS', d, 1) == ('' or 'custom')]}"
TARGET_PREFIX = "${TARGET_SYS}-"
TARGET_CC_ARCH = ""