Search through the new section containing Swift protocol descriptor
references to resolve protocols by mangled name. Use this
functionality to support protocol composition types within
_typeForMangledName.
The separate section of type references uses the same type reference format
as in protocol conformance records. As with protocol conformance records,
mangle the type reference kind into the lower two bits. Then, eliminate the
separate "flags" field from the type metadata record. Finally, rename
the section because the Swift 5 stable format for this section is
different from prior formats, and the two runtimes need to be able to
coexist.
The format of protocol conformance records will be changing in Swift 5, so
rename the segment (from, e.g., __swift2_proto to __swift5_proto) to allow
Swift < 5 and Swift 5+ runtimes to coexist.
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`.
