Bindgen-like support

[antoyo]

GCC already has -fdump-go-spec=/-fdump-ada-spec options to write Go/Ada bindings for C/C++.

-fdump-ada-spec is implemented in c-family, so in the FEs; -fdump-go-spec is in the middle-end code, hooking into debug_hooks.

[gogo2464]

assign me to this issue for the 0day hack

[GuillaumeGomez]

Done.

[gogo2464]

unsign me from this issue. it is actually not a good first issue.