If a platform removes some builtin implementations (e.g. via the
Darwin-excludes mechanism) then this can lead to test failures because
the test expects an implementation to be available.
To solve this lit features are added for each configuration based
on which sources are included in the builtin library. The features
are of the form librt_has_<name> where <name> is the name of the
source file with the file extension removed. This handles C and
With the lit features in place it is possible to make certain tests
All top-level tests in test/builtins/Unit (i.e. not under
arm, ppc, and riscv) have been annotated with the appropriate
REQUIRES: librt_has_* statement.