Maximum object file full-path length allowed by native build tools.

CMake computes for every source file an object file name that is unique to the source file and deterministic with respect to the full path to the source file. This allows multiple source files in a target to share the same name if they lie in different directories without rebuilding when one is added or removed. However, it can produce long full paths in a few cases, so CMake shortens the path using a hashing scheme when the full path to an object file exceeds a limit. CMake has a built-in limit for each platform that is sufficient for common tools, but some native tools may have a lower limit. This variable may be set to specify the limit explicitly. The value must be an integer no less than 128.