vla: evaluate operand of sizeof if its type is a vla

The c99 standard in "6.5.3.4 The sizeof operator" states:

 If the type of the operand is a variable length array type, the operand
 is evaluated;[...]

This patch mirrors the following c99 semantic in gdb:

 1| int vla[n][m];
 2| int i = 1;
 3| sizeof(vla[i++][0]); // No sideffect
 4| assert (i == 1);
 5| sizeof(vla[i++]);    // With sideffect
 6| assert (i == 2);

Note: ptype/whatis still do not allow any sideeffects.

This patch was motivated by:

  https://sourceware.org/ml/gdb-patches/2014-01/msg00732.html

gdb/ChangeLog:

	* eval.c (evaluate_subexp_for_sizeof): Add enum noside argument.
	(evaluate_subexp_standard): Pass noside argument.
	(evaluate_subexp_for_sizeof) <BINOP_SUBSCRIPT>: Handle subscript case
	if noside equals EVAL_NORMAL. If the subscript yields a vla type
	re-evaluate subscript operation with EVAL_NORMAL to enable sideffects.
	* gdbtypes.c (resolve_dynamic_bounds): Mark bound as evaluated.
	* gdbtypes.h (enum range_flags): Add RANGE_EVALUATED case.

testsuite/ChangeLog:

	* gdb.base/vla-sideeffect.c: New file.
	* gdb.base/vla-sideeffect.exp: New file.

gdb/gdbtypes.h

@@ -668,6 +668,11 @@ struct main_type
 	 subrange. This affects how the final hight bound is computed.  */
 
       int flag_upper_bound_is_count : 1;
+
+      /* True if LOW or/and HIGH are resolved into a static bound from
+	 a dynamic one.  */
+
+      int flag_bound_evaluated : 1;
     } *bounds;
 
   } flds_bnds;