Avoid quadratic strstr implementations. * lib/strstr.c: New file. * m4/strstr.m4: Likewise. * modules/strstr: Likewise. * modules/strstr-tests: Likewise. * tests/test-strstr.c: Likewise. * lib/string.in.h (rpl_strstr): Declare. (memmem) [GNULIB_POSIXCHECK]: Document speed issue. * m4/string_h.m4 (gl_HEADER_STRING_H_DEFAULTS): Support strstr. * modules/string (Makefile.am): Likewise. * MODULES.html.sh (string handling): Mention new module. * doc/functions/strstr.texi (strstr): Document the bug. Signed-off-by: Eric Blake <ebb9@byu.net>

# imaxabs.m4 serial 1
dnl Copyright (C) 2006 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_FUNC_IMAXABS],
[
  AC_REQUIRE([gl_INTTYPES_H])
  if test "$ac_cv_have_decl_imaxabs" != yes; then
    AC_LIBOBJ([imaxabs])
    gl_PREREQ_IMAXABS
  fi
])

# Prerequisites of lib/imaxabs.c.
AC_DEFUN([gl_PREREQ_IMAXABS], [:])