printf,seq,sleep,tail,timeout: accept current-locale floats

These commands now accept floating-point numbers in the
current locale, as well as in the C locale.
Compatibility problem reported by Robert Elz.
* NEWS: Document this.
* bootstrap.conf (gnulib_modules): Add cl-strtod, cl-strtold.
Remove c-strtold.
* doc/coreutils.texi (Floating point, tail invocation)
(printf invocation, timeout invocation, sleep invocation)
(seq invocation): Document this.
* gl/lib/cl-strtod.c, gl/lib/cl-strtod.h, gl/lib/cl-strtold.c:
* gl/modules/cl-strtod, gl/modules/cl-strtold: New files.
* src/printf.c, src/seq.c, src/sleep.c, src/tail.c, src/timeout.c:
Include cl-strtod.h instead of c-strtod.
* src/printf.c (vstrtold):
* src/seq.c (scan_arg, print_numbers):
* src/sleep.c (main):
* src/tail.c (parse_options):
* src/timeout.c (parse_duration):
Use cl_strtold instead of c_strtold.

gl/lib/cl-strtod.c

@@ -0,0 +1,74 @@
+/* Convert string to double in the current locale, falling back on the C locale.
+
+   Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* Written by Paul Eggert.  */
+
+#include <config.h>
+
+#include "cl-strtod.h"
+
+#include <c-strtod.h>
+
+#include <errno.h>
+#include <stdlib.h>
+
+#if LONG
+# define CL_STRTOD cl_strtold
+# define DOUBLE long double
+# define C_STRTOD c_strtold
+#else
+# define CL_STRTOD cl_strtod
+# define DOUBLE double
+# define C_STRTOD c_strtod
+#endif
+
+/* This function acts like strtod or strtold, except that it falls
+   back on the C locale if the initial prefix is not parsable in
+   the current locale.  If the prefix is parsable in both locales,
+   it uses the longer parse, breaking ties in favor of the current locale.
+
+   Parse the initial prefix of NPTR as a floating-point number in the
+   current locale or in the C locale (preferring the locale that
+   yields the longer parse, or the current locale if there is a tie).
+   If ENDPTR is not NULL, set *ENDPTR to the first unused byte, or to
+   NPTR if the prefix cannot be parsed.
+
+   If successful, return a number without changing errno.
+   If the prefix cannot be parsed, return 0 and possibly set errno to EINVAL.
+   If the number overflows, return an extreme value and set errno to ERANGE.
+   If the number underflows, return a value close to 0 and set errno to ERANGE.
+   If there is some other error, return 0 and set errno.  */
+
+DOUBLE
+CL_STRTOD (char const *nptr, char **restrict endptr)
+{
+  char *end;
+  DOUBLE d = strtod (nptr, &end);
+  if (*end)
+    {
+      int strtod_errno = errno;
+      char *c_end;
+      DOUBLE c = C_STRTOD (nptr, &c_end);
+      if (end < c_end)
+        d = c, end = c_end;
+      else
+        errno = strtod_errno;
+    }
+  if (endptr)
+    *endptr = end;
+  return d;
+}

gl/lib/cl-strtod.h

@@ -0,0 +1,2 @@
+double cl_strtod (char const *, char **restrict);
+long double cl_strtold (char const *, char **restrict);

gl/lib/cl-strtold.c

@@ -0,0 +1,2 @@
+#define LONG 1
+#include "cl-strtod.c"

gl/modules/cl-strtod

@@ -0,0 +1,24 @@
+Description:
+Convert string to double in current or C locale.
+
+Files:
+lib/cl-strtod.c
+lib/cl-strtod.h
+
+Depends-on:
+c-strtod
+
+configure.ac:
+AC_REQUIRE([AC_C_RESTRICT])
+
+Makefile.am:
+lib_SOURCES += cl-strtod.c
+
+Include:
+"cl-strtod.h"
+
+License:
+GPL
+
+Maintainer:
+all

gl/modules/cl-strtold

@@ -0,0 +1,23 @@
+Description:
+Convert string to long double in current or C locale.
+
+Files:
+lib/cl-strtold.c
+
+Depends-on:
+c-strtold
+cl-strtod
+
+configure.ac:
+
+Makefile.am:
+lib_SOURCES += cl-strtold.c
+
+Include:
+"cl-strtod.h"
+
+License:
+GPL
+
+Maintainer:
+all