arch: turn off -Werror for architectures with known warnings

A couple of architectures enable -Werror for their own files regardless of
CONFIG_WERROR but also have known warnings that fail the build with
-Wmissing-prototypes enabled by default:

arch/alpha/lib/memcpy.c:153:8: error: no previous prototype for 'memcpy' [-Werror=missing-prototypes]
arch/alpha/kernel/irq.c:96:1: error: no previous prototype for 'handle_irq' [-Werror=missing-prototypes]
arch/mips/kernel/signal.c:673:17: error: no previous prototype for ‘sys_rt_sigreturn’ [-Werror=missing-prototypes]
arch/mips/kernel/signal.c:636:17: error: no previous prototype for ‘sys_sigreturn’ [-Werror=missing-prototypes]
arch/mips/kernel/syscall.c:51:16: error: no previous prototype for ‘sysm_pipe’ [-Werror=missing-prototypes]
arch/mips/mm/fault.c:323:17: error: no previous prototype for ‘do_page_fault’ [-Werror=missing-prototypes]
arch/sparc/vdso/vma.c:246:12: warning: no previous prototype for ‘init_vdso_image’ [-Wmissing-prototypes]v
arch/sparc/vdso/vdso32/../vclock_gettime.c:343:1: warning: no previous prototype for ‘__vdso_gettimeofday_stick’ [-Wmissing-prototypes]
arch/sparc/vdso/vclock_gettime.c:343:1: warning: no previous prototype for ‘__vdso_gettimeofday_stick’ [-Wmissing-prototypes]
arch/sparc/prom/p1275.c:52:6: warning: no previous prototype for ‘prom_cif_init’ [-Wmissing-prototypes]
arch/sparc/prom/misc_64.c:165:5: warning: no previous prototype for ‘prom_get_mmu_ihandle’ [-Wmissing-prototypes]

This appears to be an artifact from the times when this architecture code
was better maintained that most device drivers and before CONFIG_WERROR
was added.  Now it just gets in the way, so remove all of these.

Powerpc and x86 both still have their own Kconfig options to enable
-Werror for some of their files.  These architectures are better
maintained than most and the options are easy to disable, so leave those
untouched.

Link: https://lkml.kernel.org/r/4be73872-c1f5-4c31-8201-712c19290a22@app.fastmail.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Stephen Rothwell <sfr@rothwell.id.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/alpha/lib/Makefile

@@ -4,7 +4,6 @@
 #
 
 asflags-y := $(KBUILD_CFLAGS)
-ccflags-y := -Werror
 
 # Many of these routines have implementations tuned for ev6.
 # Choose them iff we're targeting ev6 specifically.

arch/alpha/mm/Makefile

@@ -3,6 +3,4 @@
 # Makefile for the linux alpha-specific parts of the memory manager.
 #
 
-ccflags-y := -Werror
-
 obj-y	:= init.o fault.o

arch/mips/Kbuild

@@ -1,10 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0
-# Fail on warnings - also for files referenced in subdirs
-# -Werror can be disabled for specific files using:
-# CFLAGS_<file.o> := -Wno-error
-ifeq ($(W),)
-subdir-ccflags-y := -Werror
-endif
 
 # platform specific definitions
 include $(srctree)/arch/mips/Kbuild.platforms

arch/sparc/kernel/Makefile

@@ -5,7 +5,6 @@
 #
 
 asflags-y := -ansi
-ccflags-y := -Werror
 
 # Undefine sparc when processing vmlinux.lds - it is used
 # And teach CPP we are doing $(BITS) builds (for this case)

arch/sparc/lib/Makefile

@@ -3,7 +3,6 @@
 #
 
 asflags-y := -ansi -DST_DIV0=0x02
-ccflags-y := -Werror
 
 lib-$(CONFIG_SPARC32) += ashrdi3.o
 lib-$(CONFIG_SPARC32) += memcpy.o memset.o

arch/sparc/mm/Makefile

@@ -3,7 +3,6 @@
 #
 
 asflags-y := -ansi
-ccflags-y := -Werror
 
 obj-$(CONFIG_SPARC64)   += ultra.o tlb.o tsb.o
 obj-y                   += fault_$(BITS).o

arch/sparc/prom/Makefile

@@ -3,7 +3,6 @@
 # Linux.
 #
 asflags := -ansi
-ccflags := -Werror
 
 lib-y                 := bootstr_$(BITS).o
 lib-y                 += init_$(BITS).o