Summary:
when run "llvm-ar cr" on AIX OS , it created a gnu archive, it is not desirable in aix OS.
instead of creating a gnu archive, the patch will print a unsupport message for llvm-ar big archive write operation in AIX OS.
after implement the big archive operation, I will revert the XFAIL: AIX " and "--format=gnu" test cases in the patch.
Reviewer : James Henderson, Jinsong Ji
Differential Revision: https://reviews.llvm.org/D122746
binutils ar does not support one-dash long options (they conflict with
operation code and modifier flags).
```
% ar -help
ar: invalid option -- 'e'
...
% ar -version
ar: invalid option -- 'e'
...
% ar x --plugin=xx x.a # ok
% ar x -plugin=xx x.a
ar: two different operation options specified
% ar -plugin=/usr/lib/gcc/x86_64-linux-gnu/10/liblto_plugin.so x x.a
ar: x: No such file or directory
```
Drop one-dash long options to simplify code and match the usual practice for
command line utilities.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D116977
