PR 30308 more unbounded recursion

PR 30308 more unbounded recursion

oss-fuzz found another case where i386_intel_simplify and
i386_intel_simplify_symbol recurse until stack overflow.  This time
recursion happened on an expression with both X_add_symbol and
X_op_symbol, the call stack alternating on the two symbols.  Fix
that case too.

	* config/tc-i386-intel.c (i386_intel_simplify): Mark X_add_symbol
	whenever calling i386_intel_simplify_symbol for X_op_symbol.
	* testsuite/gas/i386/intel-equ-loop.s,
	* testsuite/gas/i386/intel-equ-loop.l: Extend testcase.