CMake: stop configuring CMAKE_INCLUDE_PATH

CMake: stop configuring CMAKE_INCLUDE_PATH

This variable affects `find_file` and `find_path`.¹ `find_file` is not used in
Graphviz and `find_path` already defaults to the correct values for the current
platform.² This change avoids, among other things, hard-coding of the target
architecture as x86-64.

Related to #1973.

¹ see https://cmake.org/cmake/help/latest/variable/CMAKE_INCLUDE_PATH.html#variable:CMAKE_INCLUDE_PATH
² https://cmake.org/cmake/help/latest/command/find_path.html#command:find_path