Use code generation to set IAMSTATIC instead of -X

Signed-off-by: Michael Hudson-Doyle <michael.hudson@linaro.org>
use code generation for GITCOMMIT/VERSION too

Signed-off-by: Michael Hudson-Doyle <michael.hudson@linaro.org>
finally, use code generation for INITSHA1 & INITPATH too

Signed-off-by: Michael Hudson-Doyle <michael.hudson@linaro.org>