CMP0040ΒΆ
Warning
The OLD behavior of this policy was removed
in CMake version 4.0.
This policy must be set to NEW by a call to
cmake_minimum_required() or cmake_policy().
The target in the TARGET signature of add_custom_command()
must exist and must be defined in the current directory.
CMake 2.8.12 and lower silently ignored a custom command created with
the TARGET signature of add_custom_command()
if the target is unknown or was defined outside the current directory.
The OLD behavior for this policy is to ignore custom commands
for unknown targets. The NEW behavior for this policy is to report
an error if the target referenced in add_custom_command() is
unknown or was defined outside the current directory.
This policy was introduced in CMake version 3.0.
Prior to removal in CMake version 4.0, it could be
set by cmake_policy() or cmake_minimum_required().
If it was not set, CMake warned, and used OLD behavior.