[llvm] [XCOFF][OBJECT] get symbol size by calling XCOFF interfaces (PR #67304)

[James Henderson via llvm-commits]

jh7370 wrote:

Some tweaks to the final message required:

> Computing the symbol size as the gap between sorted symbols is not right for XCOFF.
> For XCOFF, the size info is stored in aux symbol and can be got from the existing XCOFF interface
> getSymbolSize(). This patch changes XCOFFObjectFile to call this API to get sizes for symbols.

https://github.com/llvm/llvm-project/pull/67304