Attribute @_silgen_name is today only allowed to be used on functions, this change allows usage on globals as well. The motivation for that is to be able to "forward declare" globals just like it's today possible to do with functions (for the cases where it's not practical or convenient to use a bridging header).
Separately, this change also adds a @_silgen_name(raw: ...) syntax, which simply avoids mangling the name (by using the \01 name prefix that LLVM uses). The motivation for that is to be able to reference the "magic Darwin linker symbols" that can be used to look up section bounds (in the current dylib/module) -- those symbols don't use the underscore prefix in their mangled names.
