emit 'minifyWhitespace only in 'last' pass, to unbreak EMCC_DEBUG=2 on minified final output

emcc

@@ -1393,7 +1393,7 @@ try:
             passes = ['asmPreciseF32'] + passes
         if emit_symbol_map and 'minifyNames' in passes:
           passes += ['symbolMap='+target+'.symbols']
-        if minify_whitespace:
+        if minify_whitespace and 'last' in passes:
           passes += ['minifyWhitespace']
         logging.debug('applying js optimization passes: %s', passes)
         final = shared.Building.js_optimizer(final, passes, jcache, debug_level >= 4, js_optimizer_extra_info, just_split=just_split, just_concat=just_concat)