Fix compile warnings for CLANG compiler

Fix compile warnings for CLANG compiler

1.fix data structure redefine warnings.
2.fix 'data' with variable sized type 'union<*>' not at the end of a class warning(in immediate.hpp).
3.fix implicitly conversion warning.
4.fix explicitly assigning a variable type warning.
5.fix comparison of unsigned expression < 0 is always false warning(in cl_api.c).

Signed-off-by: Lv Meng <meng.lv@intel.com>
Reviewed-by: "Song, Ruiling" <ruiling.song@intel.com>