linux-5.4: backport ARM symbol export fix

Fixes the following warning for ARM targets:
  WARNING: "return_address" [vmlinux] is a static EXPORT_SYMBOL_GPL

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/generic/backport-5.4/040-ARM-8918-2-only-build-return_address-if-needed.patch

@@ -0,0 +1,60 @@
+From fb033c95c94ca1ee3d16e04ebdb85d65fb55fff8 Mon Sep 17 00:00:00 2001
+From: Ben Dooks <ben-linux@fluff.org>
+Date: Mon, 4 Nov 2019 18:15:15 +0100
+Subject: [PATCH] ARM: 8918/2: only build return_address() if needed
+
+The system currently warns if the config conditions for
+building return_address in arch/arm/kernel/return_address.c
+are not met, leaving just an EXPORT_SYMBOL_GPL(return_address)
+of a function defined to be 'static linline'.
+This is a result of aeea3592a13b ("ARM: 8158/1: LLVMLinux: use static inline in ARM ftrace.h").
+
+Since we're not going to build anything other than an exported
+symbol for something that is already being defined to be an
+inline-able return of NULL, just avoid building the code to
+remove the following warning:
+
+Fixes: aeea3592a13b ("ARM: 8158/1: LLVMLinux: use static inline in ARM ftrace.h")
+Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
+Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
+---
+ arch/arm/kernel/Makefile         | 6 +++++-
+ arch/arm/kernel/return_address.c | 4 ----
+ 2 files changed, 5 insertions(+), 5 deletions(-)
+
+--- a/arch/arm/kernel/Makefile
++++ b/arch/arm/kernel/Makefile
+@@ -17,10 +17,14 @@ CFLAGS_REMOVE_return_address.o = -pg
+ # Object file lists.
+
+ obj-y		:= elf.o entry-common.o irq.o opcodes.o \
+-		   process.o ptrace.o reboot.o return_address.o \
++		   process.o ptrace.o reboot.o \
+ 		   setup.o signal.o sigreturn_codes.o \
+ 		   stacktrace.o sys_arm.o time.o traps.o
+
++ifneq ($(CONFIG_ARM_UNWIND),y)
++obj-$(CONFIG_FRAME_POINTER)	+= return_address.o
++endif
++
+ obj-$(CONFIG_ATAGS)		+= atags_parse.o
+ obj-$(CONFIG_ATAGS_PROC)	+= atags_proc.o
+ obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o
+--- a/arch/arm/kernel/return_address.c
++++ b/arch/arm/kernel/return_address.c
+@@ -7,8 +7,6 @@
+  */
+ #include <linux/export.h>
+ #include <linux/ftrace.h>
+-
+-#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
+ #include <linux/sched.h>
+
+ #include <asm/stacktrace.h>
+@@ -53,6 +51,4 @@ void *return_address(unsigned int level)
+ 		return NULL;
+ }
+
+-#endif /* if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) */
+-
+ EXPORT_SYMBOL_GPL(return_address);