egrep as usual utility

[Bruno Haible]

Hi,

In make-stds.texi [1] we read:

  The @code{configure} script and the Makefile rules for building and
  installation should not use any utilities directly except these:

  @example
  awk cat cmp cp diff echo egrep expr false grep install-info ln ls
  mkdir mv printf pwd rm rmdir sed sleep sort tar test touch tr true
  @end example

Now, in the next GNU grep release, egrep will warn at each invocation [2].

Because of a portability problem to Solaris 10 [3], this means that
configure script and Makefiles should better use the EGREP variable, as
determined by the Autoconf macro AC_PROG_EGREP.

In either case, I think it's now time to remove 'egrep' from the list of
usual utilities.

Opinions?

Bruno

[1] https://www.gnu.org/prep/standards/html_node/Utilities-in-Makefiles.html
[2] 
https://git.savannah.gnu.org/gitweb/?p=grep.git;a=commitdiff;h=a9515624709865d480e3142fd959bccd1c9372d1
[3] https://lists.gnu.org/archive/html/bug-standards/2020-12/msg00004.html