Restructure the COFF metadata handling to use the linker section
grouping to emit section start/stop markers in the appropriate location.
This allows us to lookup the sections statically without having to the
walk the entire image structure.
Introduce a constructor for PE/COFF binaries. This will ensure that the
registration occurs for all modules appropriately. This should resolve
rdar://problem/19045112. The registration should occur prior to
`DllMain` being invoked from `DllMainCRTStartup`.
