[MC] Produce proper section relative relocations for COFF in .debug_frame

The third parameter to Streamer.EmitSymbolValue() is "bool
IsSectionRelative = false".

For ELF, these debug sections are mapped to address zero, so a normal,
absolute address relocation works just fine, but COFF needs a section
relative relocation, and COFF is the only target where
needsDwarfSectionOffsetDirective() returns true. This matches how
EmitSymbolValue is called elsewhere in the same source file.

Differential Revision: https://reviews.llvm.org/D70661