HoughFstat: fix build errors

Description

This MR should fix the build errors here.

• Remove unused variables in HoughFstat/LocalComputeFstatHoughMap.c (cf 7ba81f9e)
• hough_x64.i was missing some MacOS-specific definitions, which I copied from the identical definitions in hough_{sse2|x87}.i

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

Review Status

N/A