I'm not aware of any way for `%run` wrapper scripts like
`iosssim_run.py`
([ref](d2c7c60642/compiler-rt/test/sanitizer_common/ios_commands/iossim_run.py (L4)))
to know what testcase they are currently running. This can be useful if
these wrappers need to create a (potentially remote) temporary directory
for each test case.
This adds the `LIT_CURRENT_TESTCASE` environment variable to both the
internal shell and the external shell, containing the full name of the
current test being run.
3f6cbdea4f