[lit][tests][AIX] Update expected form of diagnostic messages; use `not` to…


[lit][tests][AIX] Update expected form of diagnostic messages; use not to normalize non-zero exit values

Various tests in the lit testing suite expect specific return codes
and forms of diagnostic message from utility programs. As per
POSIX.1-2017 XCU Section 1.4, Utility Description Defaults, "[the]
format of diagnostic messages for most utilities is unspecified".
The STDERR subsections of the cat and wc utilities merely indicate
that "[the] standard error shall be used only for diagnostic messages".
The corresponding EXIT STATUS subsections merely indicate, with regard
to errors, an exit value of >0.

The affected tests are updated to accept the applicable diagnostic
message as produced by the utilities on AIX. The exit value is
normalized using not as necessary.

Reviewers: xingxue, sfertile, jasonliu

Reviewed By: xingxue

Subscribers: delcypher, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60553