importc not generated for typedef

[arnetheduck]

typedef void (*some_proc)(const void *key);

void xxx(some_proc p);

type
  SomeProc* = proc (key: pointer) {.cdecl.}

proc xxx*(p: SomeProc) {.cdecl, importc: "xxx", header: "test.h".}

importc here is needed to ensure that the C typedef is used where relevant, and not the thing that Nim thinks is equivalent: Nim lacks the language to represent const void* correctly - this leads to compile issues down the line with const-vs-non-const type problems.

The above should be SomeProc* {.importc: "some_proc", header: "test.h".} = proc (key: pointer) {.cdecl.}