Fix the build of OpenCV with XIMEA on Windows 64 bits:
  - crosses initializations in "cap_ximea.cpp" (which also contained some awfull "goto" instructions)
  - the "CMAKE_CL_64" variable is not initialized when using mingw

PR#1039 modified to be able to merge on branch 2.4
Trailing whitespace removal.
Using four spaces for indentation.
Back to the previous coding way (using the macro with the goto).
Merge pull request #1776 from philippefoubert:merge_upstream_2.4_ximea