[XCOFF][NFC] make StorageMappingClass/SymbolType member optional

This patch makes StorageMappingClass/SymbolType member optional in
class MCSectionXCOFF.

Non-csect sections like debug sections have no such properties.

Reviewed By: hubert.reinterpretcast

Differential Revision: https://reviews.llvm.org/D96641

GitOrigin-RevId: 4c23707a418add9c584af5247faa5a9527632a0c
2 files changed