Computing the symbol size as the gap between sorted symbols are not
right for XCOFF.
For XCOFF, the size info is stored in aux symbol and can be got from
existing XCOFF interface `getSymbolSize()`.
This patch changes XCOFFObjectFile to call this API to get sizes for
symbols.
For now, data location expression is hard coded to little endian. We are
going to support sanitizers on AIX which is big endian. Support big
endian too in the data location expression parser of llvm-symbolizer.