[libc][NFC] Extend ErrnoSetterMatcher to test expected inequalities. (#67153)

Before this change, ErrnoSetterMatcher only allowed testing for equality
of the expected return and errno values. This change extends it to allow
testing for expected inequalities of the return and errno values. The
test libc.test.src.stdio.fileop_test has been updated to use the
ErrnoSetterMatcher with tests for inequalities.