Fix decodes on 64-bit devices built with clang-3.8

Mark the variable "status" in WebPParseHeaders as volatile. There
appears to be a bug in clang that requires this. See b/25845393 for
more info.

BUG:25845393
BUG:25787662
BUG:25793249
Change-Id: I2fbee461b3448bf5662b8234a48e9a158adfc6b0
2 files changed