Function pointers get converted to `ptr FunctionType` instead of just `FunctionType`

[ghost]

Futhark converts C definitions of function pointers inside structs that are defined as separate types to ptr FunctionType instead of just FunctionType.

For example with this C header:

typedef int PDCallbackFunction(void* userdata); // return 0 when done

struct playdate_sys
{
	void (*setUpdateCallback)(PDCallbackFunction* update, void* userdata);
};

Futhark makes this:

from macros import hint

type
  Pdcallbackfunction_436207905* = proc (a0: pointer): cint {.cdecl.} ## Generated based on /home/dian/Projects/NimExperiments/api/testheader.h:1:13
  structplaydatesys_436207908* = object
    setupdatecallback*: proc (a0: ptr Pdcallbackfunction_436207907; a1: pointer): void {.
        cdecl.}              ## Generated based on /home/dian/Projects/NimExperiments/api/testheader.h:3:8
  
  Pdcallbackfunction_436207907* = (when declared(Pdcallbackfunction):
    Pdcallbackfunction
   else:
    Pdcallbackfunction_436207905)
  structplaydatesys_436207909* = (when declared(structplaydatesys):
    structplaydatesys
   else:
    structplaydatesys_436207908)
when not declared(Pdcallbackfunction):
  type
    Pdcallbackfunction* = Pdcallbackfunction_436207905
else:
  static :
    hint("Declaration of " & "PDCallbackFunction" &
        " already exists, not redeclaring")
when not declared(structplaydatesys):
  type
    structplaydatesys* = structplaydatesys_436207908
else:
  static :
    hint("Declaration of " & "struct_playdate_sys" &
        " already exists, not redeclaring")