btrfs: Mark btrfs_assertfail() __noreturn

Fixes a bunch of warnings including:

  vmlinux.o: warning: objtool: select_reloc_root+0x314: unreachable instruction
  vmlinux.o: warning: objtool: finish_inode_if_needed+0x15b1: unreachable instruction
  vmlinux.o: warning: objtool: get_bio_sector_nr+0x259: unreachable instruction
  vmlinux.o: warning: objtool: raid_wait_read_end_io+0xc26: unreachable instruction
  vmlinux.o: warning: objtool: raid56_parity_alloc_scrub_rbio+0x37b: unreachable instruction
  ...
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/960bd9c0c9e3cfc409ba9c35a17644b11b832956.1681342859.git.jpoimboe@kernel.org

fs/btrfs/messages.c

@@ -253,7 +253,7 @@ void __cold _btrfs_printk(const struct btrfs_fs_info *fs_info, const char *fmt,
 #endif
 
 #ifdef CONFIG_BTRFS_ASSERT
-void __cold btrfs_assertfail(const char *expr, const char *file, int line)
+void __cold __noreturn btrfs_assertfail(const char *expr, const char *file, int line)
 {
 	pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
 	BUG();

fs/btrfs/messages.h

@@ -160,7 +160,7 @@ do {								\
 } while (0)
 
 #ifdef CONFIG_BTRFS_ASSERT
-void __cold btrfs_assertfail(const char *expr, const char *file, int line);
+void __cold __noreturn btrfs_assertfail(const char *expr, const char *file, int line);
 
 #define ASSERT(expr)						\
 	(likely(expr) ? (void)0 : btrfs_assertfail(#expr, __FILE__, __LINE__))

tools/objtool/check.c

@@ -204,6 +204,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 		"__ubsan_handle_builtin_unreachable",
 		"arch_call_rest_init",
 		"arch_cpu_idle_dead",
+		"btrfs_assertfail",
 		"cpu_bringup_and_idle",
 		"cpu_startup_entry",
 		"do_exit",