scripts: fix missing space when using CT_EXTRA_FLAGS_FOR_HOST

CT_EXTRA_FLAGS_FOR_HOST needs a preceding space to separate it from
any other options that have already been set.

Signed-off-by: Michael Hope <michael.hope@linaro.org>

 # Alpha specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_USE_MMU

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ##

 ## help The Alpha architecture.