package, such as C.puts. It collects all such identifiers. The next
step is to determine each kind of name. In C.xxx the xxx might refer
to a type, a function, a constant, or a global variable. Cgo must
decide which.

The obvious thing for cgo to do is to process the preamble, expanding
#includes and processing the corresponding C code. That would require
a full C parser and type checker that was also aware of any extensions