x86: handle SVR4 escaped binary operators

x86: handle SVR4 escaped binary operators

PR gas/4572

When / is a comment character, its use as binary "divide" operator needs
escaping by a backslash. Besides the scrubber needing to support this
(addressed in an earlier change), there are also a few provisions needed
in target specific operator handling.

As the spec calls for % and * to also be escaped because of being
"overloaded", also recognize these, despite the overloading there not
really preventing their use as operators in most (%) or all (*) cases,
given the way how the rest of the assembler works.

To bring source and testsuite in line, also drop the TE_I386AIX part of
the respective conditional, as i?86-*-aix* support had been removed a
while ago.