gas support for AIX visibility

[Ådne Hovda]

Hi

I ran into this error building my AIX 5.3 cross-compiler (since gcc 7) 
during the libgcc stage:

/tmp/ccm6OmNp.s: Assembler messages:
/tmp/ccm6OmNp.s:445: Error: junk at end of line, first unrecognized 
character is `,'

gas does not like this line, it has an extra field:

         .comm __gcov_time_profiler_counter,8,3,hidden

 From the xlC docs: 
https://www.ibm.com/developerworks/aix/library/au-aix-symbol-visibility-part2/index.html

Listing 14. Syntax for specifying visibility attribute in assembly
    .extern Name [ , Visibility ]
    .globl  Name [ , Visibility ]
    .weak   Name [ , Visibility ]
    .comm   Name, Expression [, Number [, Visibility ] ]

Just a heads up, I have no idea how and if this should be fixed and I 
can still use my existing toolchain.

BR,
Ã
dne Hovda