bcachefs: Plumb more logging through stdio redirect

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index 33605fa..e0e9afb 100644
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -267,6 +267,8 @@ do {									\
 
 #define bch2_fmt(_c, fmt)		bch2_log_msg(_c, fmt "\n")
 
+void bch2_print_str(struct bch_fs *, const char *);
+
 __printf(2, 3)
 void bch2_print_opts(struct bch_opts *, const char *, ...);