Make libc unittests hermetic wrt modifying errno #59276
Description
A good number of libc unittests and integration tests set/reset errno. Often, it is the app wide errno that is modified. This is OK as long as the tests run in their own process. However, on certain platforms, all libc unittests are run in a single process one after the other. If the unittest author misses resetting the errno at the right places, then the unittests cease to be hermetic. This tracker is about making the unittests hermetic wrt errno. Once approach we can take is to handout each test its own errno. This way, the errno modified in one test does not affect the errno of another test.