x86/entry: Move thunk restore code into thunk functions

There's no need for both thunk functions to jump to the same shared
thunk restore code which lives outside the thunk function boundaries.
It disrupts i-cache locality and confuses objtool.  Keep it simple by
keeping each thunk's restore code self-contained within the function.

Fixes a bunch of false positive "missing __noreturn" warnings like:

  vmlinux.o: warning: objtool: do_arch_prctl_common+0xf4: preempt_schedule_thunk() is missing a __noreturn annotation

Fixes: fedb724c ("objtool: Detect missing __noreturn annotations")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202305281037.3PaI3tW4-lkp@intel.com/
Link: https://lore.kernel.org/r/46aa8aeb716f302e22e1673ae15ee6fe050b41f4.1685488050.git.jpoimboe@kernel.orgSigned-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

arch/x86/entry/thunk_64.S

@@ -26,17 +26,7 @@ SYM_FUNC_START(\name)
 	pushq %r11
 
 	call \func
-	jmp  __thunk_restore
-SYM_FUNC_END(\name)
-	_ASM_NOKPROBE(\name)
-	.endm
-
-	THUNK preempt_schedule_thunk, preempt_schedule
-	THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
-	EXPORT_SYMBOL(preempt_schedule_thunk)
-	EXPORT_SYMBOL(preempt_schedule_notrace_thunk)
 
-SYM_CODE_START_LOCAL(__thunk_restore)
 	popq %r11
 	popq %r10
 	popq %r9
@@ -48,5 +38,11 @@ SYM_CODE_START_LOCAL(__thunk_restore)
 	popq %rdi
 	popq %rbp
 	RET
-	_ASM_NOKPROBE(__thunk_restore)
-SYM_CODE_END(__thunk_restore)
+SYM_FUNC_END(\name)
+	_ASM_NOKPROBE(\name)
+	.endm
+
+THUNK preempt_schedule_thunk, preempt_schedule
+THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
+EXPORT_SYMBOL(preempt_schedule_thunk)
+EXPORT_SYMBOL(preempt_schedule_notrace_thunk)