gas: leave expression symbols alone when processing equates
PR gas/32721
In this bogus piece of code distilled from fuzzing and slightly edited:
A=%eax|%!
Y=A
Z=A
or $6,Z
the first of the equates with A on the rhs changes A's section (due to
the use of S_GET_VALUE()), from expression to register, thus yielding Y
in the expression section (and X_op being O_symbol), but Z in the
register section (and X_op being O_register with X_add_value being -1).
There shouldn't be random O_register expressions, though, for targets
setting md_register_arithmetic to false. Plus both Y and Z would better
be exchangeable.
In pseudo_set() wire handling of O_symbol expressions referencing a
symbol in the expression section to that of other stuff ending up in
this section.
Also avoid bogus O_register expressions to be created, for targets
setting md_register_arithmetic to false: S_GET_VALUE() would resolve
any arithmetic, which must not happen for such targets. To be on the
safe side for such targets, also amend resolve_register(). Correct
another earlier oversight there too (affecting at least Z80), by using
the new expr_copy() helper there as well.
Undo
46b9f07dfe79 ("PR 32721, internal error in
tc-i386.c:parse_register"), albeit without losing the simplification it
did.