CMake/Help/variable/CMAKE_USER_MAKE_RULES_OVERRIDE.rst

CMAKE_USER_MAKE_RULES_OVERRIDE
------------------------------

Specify a CMake file that overrides platform information.

CMake loads the specified file while enabling support for each
language from either the project() or enable_language() commands.  It
is loaded after CMake's builtin compiler and platform information
modules have been loaded but before the information is used.  The file
may set platform information variables to override CMake's defaults.

This feature is intended for use only in overriding information
variables that must be set before CMake builds its first test project
to check that the compiler for a language works.  It should not be
used to load a file in cases that a normal include() will work.  Use
it only as a last resort for behavior that cannot be achieved any
other way.  For example, one may set CMAKE_C_FLAGS_INIT to change the
default value used to initialize CMAKE_C_FLAGS before it is cached.
The override file should NOT be used to set anything that could be set
after languages are enabled, such as variables like
CMAKE_RUNTIME_OUTPUT_DIRECTORY that affect the placement of binaries.
Information set in the file will be used for try_compile and try_run
builds too.