Enable build flag to show build warning

Enable build flag to show build warning

[Issue#]   N/A
[Problem]  Build flag to show build warning isn't enabled.
           - As build warning is helpful to find bug in the build time,
             enable build flag to show build warning.
[Cause]    N/A
[Solution] Add build flag regarding build warning.

           http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
           - ADD_DEFINITIONS("-Wall")
             This enables all the warnings about constructions that some users consider questionable,
             and that are easy to avoid (or modify to prevent the warning),
             even in conjunction with macros.
             This also enables some language-specific warnings described
             in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options.
          - ADD_DEFINITIONS("-Wextra")
            This enables some extra warning flags that are not enabled by -Wall.
            (This option used to be called -W.
             The older name is still supported, but the newer name is more descriptive.)
[SCMRequest] N/A

Change-Id: If7ccc284b49cdcb72623b8c1c824aa6166631122