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>

# mathl.m4 serial 4
dnl Copyright (c) 2003, 2007 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_LONG_DOUBLE_MATH], [

AC_CHECK_LIB(m, atan)
AC_REPLACE_FUNCS(floorl ceill sqrtl asinl acosl atanl \
        logl expl tanl sinl cosl)

])