libgcc: add forward declarations for generic library routines

With W=1 on platforms that use the generic gcc library routines
(csky/loongarch/mips/riscv/sh/xtensa):

lib/ashldi3.c:9:19: warning: no previous prototype for '__ashldi3' [-Wmissing-prototypes]
9 | long long notrace __ashldi3(long long u, word_type b)
| ^~~~~~~~~
CC lib/ashrdi3.o
lib/ashrdi3.c:9:19: warning: no previous prototype for '__ashrdi3' [-Wmissing-prototypes]
9 | long long notrace __ashrdi3(long long u, word_type b)
| ^~~~~~~~~
CC lib/cmpdi2.o
lib/cmpdi2.c:9:19: warning: no previous prototype for '__cmpdi2' [-Wmissing-prototypes]
9 | word_type notrace __cmpdi2(long long a, long long b)
| ^~~~~~~~
CC lib/lshrdi3.o
lib/lshrdi3.c:9:19: warning: no previous prototype for '__lshrdi3' [-Wmissing-prototypes]
9 | long long notrace __lshrdi3(long long u, word_type b)
| ^~~~~~~~~
CC lib/muldi3.o
lib/muldi3.c:49:19: warning: no previous prototype for '__muldi3' [-Wmissing-prototypes]
49 | long long notrace __muldi3(long long u, long long v)
| ^~~~~~~~
CC lib/ucmpdi2.o
lib/ucmpdi2.c:8:19: warning: no previous prototype for '__ucmpdi2' [-Wmissing-prototypes]
8 | word_type notrace __ucmpdi2(unsigned long long a, unsigned long long b)
| ^~~~~~~~~

Fix this by adding forward declarations to the common libgcc header
file.

Link: https://lkml.kernel.org/r/5cdbe08296693dd53849f199c3933e16e97b33c1.1682088593.git.geert+renesas@glider.be
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202303272214.RxzpA6bP-lkp@intel.com/
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 120

Based on 1 normalized pattern(s):

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 2 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 the file copying or write to the free
software foundation inc

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 12 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190523091651.231300438@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

move libgcc.h to include/linux

Introducing a new include/lib directory just for this file totally
messes up tab completion for include/linux, which is highly annoying.

Move it to include/linux where we have headers for all kinds of other
lib/ code as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>