bug#57116: cling: missing some system header files

[Gang Liang <randomizedthinking@gmail.com>]

I had a fresh installation of cling from guix, and got the following
error. Seems some system headers are missing.

Tried it on two machines, and both had the same problem.

****************** CLING ******************
* Type C++ code and press enter to run it *
*             Type .q to exit             *
*******************************************
[cling]$ #include <iostream>
In file included from input_line_3:1:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/iostream:39:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/ostream:38:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/ios:42:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/bits/ios_base.h:41:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/bits/locale_classes.h:40:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/string:55:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/bits/basic_string.h:6545:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/ext/string_conversions.h:44:
In file included from
/gnu/store/069aq2v993kpc41yabp5b6vm4wb9jkhg-gcc-10.3.0/include/c++/cerrno:42:
In file included from
/gnu/store/5h2w4qi9hk1qzzgi1w83220ydslinr4s-glibc-2.33/include/errno.h:28:
/gnu/store/5h2w4qi9hk1qzzgi1w83220ydslinr4s-glibc-2.33/include/bits/errno.h:26:11:
fatal error: 'linux/errno.h' file not found
# include <linux/errno.h>
          ^~~~~~~~~~~~~~~