* stmt.c (n_occurrences): New static function.
(expand_asm_operands): Verify that all constrains match in the
number of alternatives.
Verify that '+' or '=' are at the beginning of an output constraint.
Don't allow '&' for input operands.
Verify that '%' isn't written for the last operand.
* reload.c (find_reloads): Abort if an asm is found with invalid
constraints; all possible problems ought to be checked for earlier.