PR23800, .eqv doesn't always defer expression evaluation

PR23800, .eqv doesn't always defer expression evaluation

.eqv (and ==) ought not simplify expressions involving dot or other
symbols set by .eqv.  If such simplification occurs, the value of dot
will be that at the assignment rather than at the place where the
symbol is used.

	PR 23800
	* expr.c (expr): Don't simplify expressions involving forward_ref
	symbols when mode is expr_defer.
	* config/tc-spu.c (spu_cons): Parse expression using normal
	expression evaluation if @ppu is not detected.
	* testsuite/gas/all/eqv-dot.d,
	* testsuite/gas/all/eqv-dot.s: New test.
	* testsuite/gas/all/gas.exp: Run it.