Improve converted names for arithmetic operators

[pdarragh]

If symbol->label is used on names like +, you end up with label___12345, which is very unhelpful. Maybe we could incorporate special-case names for certain common symbols, depending on what the nasm specification allows.

www/langs/a86/ast.rkt

Lines 400 to 421 in 7f55e4f

	;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
	;; Symbol to Label
	;; Symbol -> Label
	;; Produce a symbol that is a valid Nasm label
	;; Guarantees that (eq? s1 s2) <=> (eq? (symbol->label s1) (symbol->label s1))
	(provide symbol->label)
	(define (symbol->label s)
	(string->symbol
	(string-append
	"label_"
	(list->string
	(map (λ (c)
	(if (or (char<=? #\a c #\z)
	(char<=? #\A c #\Z)
	(char<=? #\0 c #\9)
	(memq c '(#\_ #\$ #\# #\@ #\~ #\. #\?)))
	c
	#\_))
	(string->list (symbol->string s))))
	"_"
	(number->string (eq-hash-code s) 16))))