rdstdin (linenoise) breaks the C++ backend

[HJarausch]

import rdstdin
echo "Merry Christmas"
let ans= readLineFromStdin("do you follow the Corona rules ")
if ans != "yes" :
  echo "but you should!"
else :
  echo "fine"

#[
Compiling this with nim cpp -r Hello.nim
gives
/usr/lib/nim/wrappers/linenoise/linenoise.c: In function 'void abAppend(abuf*, const char*, int)':
/usr/lib/nim/wrappers/linenoise/linenoise.c:462:11: error: expected unqualified-id before 'new'
462 | char *new = realloc(ab->b,ab->len+len);
| ^~~
/usr/lib/nim/wrappers/linenoise/linenoise.c:464:13: error: expected type-specifier before '==' token
464 | if (new == NULL) return;
| ^~
/usr/lib/nim/wrappers/linenoise/linenoise.c:465:15: error: expected type-specifier before '+' token
465 | memcpy(new+ab->len,s,len);
| ^
]#

**new** is a keyword in C++ and must not be used as an identifier.
linenoise.c should be fixed to be valid C++ .
e.g. by applying the attached patch
[linenoise.c.diff.txt](https://github.com/nim-lang/Nim/files/5735670/linenoise.c.diff.txt)

Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2020-12-23
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: b1c3dab2089bb4327627c2152a1148b299f1a930
active boot switches: -d:release
5

[ringabout]

see #3720
and antirez/linenoise#87

[ringabout]

Note that

This module contains code for reading from stdin:idx:. On UNIX the
linenoise library is wrapped and set up to provide default key bindings
(e.g. you can navigate with the arrow keys). On Windows system.readLine
is used. This suffices because Windows' console already provides the
wanted functionality.

nim cpp works in windows since system.readLine is used.

[ringabout]

PR is welcome

[timotheecour]

proposed approach to fix this: see #16451 (comment)

[timotheecour]

@HJarausch I can't reproduce

on osx: works
(fee5fbc 1.5.1 and also 1.4.2 work)

on linux: works

ya works for me on linux too w 1.5.1
d34d023
g++
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)

command:
nim r -b:cpp main

[krux02]

I have a déjà vu here. This discussion has been there in the past. It had been resolved. The problem was fixed. This is a regression.
#5357 (comment)

[ringabout]

If someone can reproduce this issue, feel free to reopen.