The asset system and supporting libraries were using off_t instead of
off64_t to access files larger than 2GB (32-bit signed). This change
replaces all off_t with off64_t and lseek64.
There is a new utils/Compat.h added for Mac OS compatibility.
Also fixed some size-related compiler warnings.
Bug: 3205336
Change-Id: I9097b3cb7a602e811fe52f245939d8975da55e9e