i#1577 use-of-uninitialized-variable: use union as workaround
i#1577 use-of-uninitialized-variable: use union as workaround

core/arch/x86_code.c:446:5: error: ‘*(&var+-1)’ is used uninitialized in this function [-Werror=uninitialized]
     memcpy(&var, &var-1, 1); /* avoid uninit warning */

Fixes #1577
Review-URL: https://codereview.appspot.com/191320043

code4bones/dynamorio,daksunt/dynamorio,sigma-random/dynamorio,sigma-random/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,code4bones/dynamorio,sigma-random/dynamorio,daksunt/dynamorio,sigma-random/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,bl4ckic3/dynamorio,bl4ckic3/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,code4bones/dynamorio,code4bones/dynamorio,daksunt/dynamorio,bl4ckic3/dynamorio,AmesianX/dynamorio,sigma-random/dynamorio,code4bones/dynamorio,AmesianX/dynamorio