Warning in gcc/libiberty/dyn-string.c during build

[nick <xerofoify@gmail.com>]

Greetings all,
I just got this in my build output:
ar: `u' modifier ignored since `D' is the default (see `U')                                                                                                                    
configure: WARNING: cannot check for properly working vsnprintf when cross compiling, will assume it's ok                                                                      
../../gcc/libiberty/dyn-string.c: In function ‘dyn_string_insert_cstr’:                                                                                                        
 ../../gcc/libiberty/dyn-string.c:280:3: warning: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]   
 strncpy (dest->s + pos, src, length);                                                                                                                                
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                 
 ../../gcc/libiberty/dyn-string.c:272:16: note: length computed here                                                                                                            
272 |   int length = strlen (src);                                                                                                                                           
|                ^~~~~~~~~~~~                                                                                                                                            
 ../../gcc/libiberty/dyn-string.c: In function ‘dyn_string_insert_cstr’:                                                                                                        
\ ../../gcc/libiberty/dyn-string.c:280:3: warning: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]   
280 |   strncpy (dest->s + pos, src, length);                                                                                                                                
|   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                                                                                                                                 
 ../../gcc/libiberty/dyn-string.c:272:16: note: length computed here                                                                                                            
272 |   int length = strlen (src);                                                                                                                                           
|                ^~~~~~~~~~~~    

I've already looked through git blame and it seems this code was last touched in 2000. That warning seems
to be  new to gcc 8 after a little research so is this a rather old bug that was not found and very
subtle or is this a mislabel. Seems to be a mislabel to me but I'm new to the code base so just thought
I would ask.

Cheers,
Nick