sh: define RUNTIME_DISCARD_EXIT

sh vmlinux fails to link with GNU ld < 2.40 (likely < 2.36) since
commit 99cb0d9 ("arch: fix broken BuildID for arm64 and riscv").

This is similar to fixes for powerpc and s390:
commit 4b9880d ("powerpc/vmlinux.lds: Define RUNTIME_DISCARD_EXIT").
commit a494398 ("s390: define RUNTIME_DISCARD_EXIT to fix link error
with GNU ld < 2.36").

  $ sh4-linux-gnu-ld --version | head -n1
  GNU ld (GNU Binutils for Debian) 2.35.2

  $ make ARCH=sh CROSS_COMPILE=sh4-linux-gnu- microdev_defconfig
  $ make ARCH=sh CROSS_COMPILE=sh4-linux-gnu-

  `.exit.text' referenced in section `__bug_table' of crypto/algboss.o:
  defined in discarded section `.exit.text' of crypto/algboss.o
  `.exit.text' referenced in section `__bug_table' of
  drivers/char/hw_random/core.o: defined in discarded section
  `.exit.text' of drivers/char/hw_random/core.o
  make[2]: *** [scripts/Makefile.vmlinux:34: vmlinux] Error 1
  make[1]: *** [Makefile:1252: vmlinux] Error 2

arch/sh/kernel/vmlinux.lds.S keeps EXIT_TEXT:

	/*
	 * .exit.text is discarded at runtime, not link time, to deal with
	 * references from __bug_table
	 */
	.exit.text : AT(ADDR(.exit.text)) { EXIT_TEXT }

However, EXIT_TEXT is thrown away by
DISCARD(include/asm-generic/vmlinux.lds.h) because
sh does not define RUNTIME_DISCARD_EXIT.

GNU ld 2.40 does not have this issue and builds fine.
This corresponds with Masahiro's comments in a494398:
"Nathan [Chancellor] also found that binutils
commit 21401fc7bf67 ("Duplicate output sections in scripts") cured this
issue, so we cannot reproduce it with binutils 2.36+, but it is better
to not rely on it."

Link: https://lkml.kernel.org/r/9166a8abdc0f979e50377e61780a4bba1dfa2f52.1674518464.git.tom.saeger@oracle.com
Fixes: 99cb0d9 ("arch: fix broken BuildID for arm64 and riscv")
Link: https://lore.kernel.org/all/[email protected]/
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Tom Saeger <[email protected]>
Tested-by: John Paul Adrian Glaubitz <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Dennis Gilmore <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Naresh Kamboju <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Rich Felker <[email protected]>
Cc: Yoshinori Sato <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: tsaeger

arch/sh/kernel/vmlinux.lds.S

@@ -4,6 +4,7 @@
  * Written by Niibe Yutaka and Paul Mundt
  */
 OUTPUT_ARCH(sh)
+#define RUNTIME_DISCARD_EXIT
 #include <asm/thread_info.h>
 #include <asm/cache.h>
 #include <asm/vmlinux.lds.h>