Use C function pointer argument names in proc types

[jon-edward]

Currently, futhark replaces argument names of function pointers with a[some number].

This can be seen with the simple example:

// ./include/testlib.h

typedef struct ContainsFunctionPointer {
    int (*myFunc)(int descriptiveParameter1, int descriptiveParameter2);
} ContainsFunctionPointer;

# ./test.nim

import std/os

import futhark

const currentDir = currentSourcePath.parentDir

importc:
    outputPath currentDir / "generated.nim"
    path currentDir / "include"
    "testLib.h"

The result of generated.nim after nim r -d:nodeclguards ./test.nim (no declaration guards for readability, the existence or nonexistence of this flag does not change the resulting type):

# ./generated.nim

type
  struct_ContainsFunctionPointer* {.pure, inheritable, bycopy.} = object
    myFunc*: proc (a0: cint; a1: cint): cint {.cdecl.}
  ContainsFunctionPointer* = struct_ContainsFunctionPointer

It might be nicer for library usage if the resulting generated.nim was something more like:

type
  struct_ContainsFunctionPointer* {.pure, inheritable, bycopy.} = object
    myFunc*: proc (descriptiveParameter1: cint; descriptiveParameter2: cint): cint {.cdecl.}
  ContainsFunctionPointer* = struct_ContainsFunctionPointer

For users of the wrapper, it will offer more insight into what kind of objects should be passed to procs (more than just type information).

[jon-edward]

This seems to be an issue with opir, perhaps at

futhark/src/opir.nim

Lines 322 to 326 in 783f2af

	var aname = ""
	if funcDecl.isSome:
	aname = funcDecl.get.Cursor_getArgument(i).getName
	if aname == "":
	aname = "a" & $i

[AmjadHD]

This needs to be passed a cursor

futhark/src/opir.nim

Lines 126 to 127 in 8b55098

	of CXType_FunctionProto, CXType_FunctionNoProto:
	ct.genProcDecl()