added warning flag to gcc config and eliminated warning related to jmp_buf initialization
added warning flag to gcc config and eliminated warning related to jmp_buf initialization

git-svn-id: 45b91d5ffbe0aac29cbe3db7b8820ea1f7865447@26 e7d17a6e-8845-0410-bbbc-c8efb4fdad7e

ARMmbed/unity