Fix read to stdout output appearing first

echo banana (read)

will output whatever read reads _first_ because it uses a direct
write_loop().

This also removes some duplicate code.

src/builtin_read.cpp

@@ -394,11 +394,6 @@ static int validate_read_args(const wchar_t *cmd, read_cmd_opts_t &opts, int arg
     return STATUS_CMD_OK;
 }
 
-void write_stdout(wcstring val) {
-    const std::string &out = wcs2string(val);
-    write_loop(STDOUT_FILENO, out.c_str(), out.size());
-}
-
 /// The read builtin. Reads from stdin and stores the values in environment variables.
 int builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     wchar_t *cmd = argv[0];
@@ -446,7 +441,7 @@ int builtin_read(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
     }
 
     if (opts.to_stdout) {
-        write_stdout(buff);
+        streams.out.append(buff);
         return exit_res;
     }
 

tests/read.in

@@ -247,3 +247,7 @@ begin
     echo a...b...c | read -l a b c
     echo $a; echo $b; echo $c
 end
+echo
+
+# At one point, whatever was read was printed _before_ banana
+echo banana (echo sausage | read)

tests/read.out

@@ -130,3 +130,5 @@ Multi-char delimiters with IFS
 a
 b
 ..c
+
+banana sausage