PR libc/3606: Correcting the locale.texi documentation

[Petter Reinholdtsen]

The bug report comment on the following part of the glibc manual.

  The glibc manual says ("Categories of Activities that Locales Affect"):
 
  `LC_ALL'
       This is not an environment variable; it is only a macro that you
       can use with `setlocale' to set a single locale for all purposes.
       Setting this environment variable overwrites all selections by the
       other `LC_*' variables or `LANG'.

As far as I can see, LC_ALL is fetched from the environment, and thus
is an environment variable:

  % LANG=C LC_ALL=nn_NO locale charmap
  ISO-8859-1
  % LANG=nn_NO LC_ALL=C locale charmap
  ANSI_X3.4-1968

What is the documentation ment to say?