Instead of putting the magic in the AST, generate regular accessor
methods. This avoids a number of special cases in the compiler, and
avoids missing any of them.
The resulting union accesses are somewhat clunkier to use, but the
compiler implementation has far less coupling between the CGo
implementation and the IR generator.
Not all enums may be used as a type anywhere, which was previously the
only way to include an enum in the AST. This commit makes sure all enums
are included.
This commit renames reserved field names like `type` to `_type`, and in
turn renames those fields as well (recursively). This avoids name
clashes when a C struct contains a field named `type`, which is a
reserved keyword in Go.
For some details, see:
https://golang.org/cmd/cgo/#hdr-Go_references_to_C
