Do pass NO_CMAKE_FIND_ROOT_PATH to find_file for files in build directory
Without this find_file would never attempt to search the build directory
if CMAKE_FIND_ROOT_PATH
is set to a cross root filesystem, which the
build_directory is not an ancestor of.
I'm also wondering, why find_file was chosen here in the first place, instead of just hard-coding the path to
${CMAKE_SOURCE_DIR}/cmake/modules/sip-generate.py
and ${CMAKE_SOURCE_DIR}/cmake/modules/pyproject.toml.in
since I doubt that we have to expect sudden fluctuations of the locations of these files.