[latex][bugfix][win32][cmake] ignore CMAKE_FIND_ROOT_PATH for latexmkrc.cmake
When cross compiling for windows it is necessary to tweak CMAKE_FIND_ROOT_PATH_MODE_* to modify default behavior of FIND_XXX() commands to search for headers/libs in the target environment and search for programs in the build host environment.
This lead to a problem when searching for latexmkrc.cmake.
We now explicitly change the UseLatexMk find_file call to ignore the CMAKE_FIND_ROOT_PATH and thus beeing able to find the file in the source directory.
@gruenich can we backport this to 2.7?