[PATCH] use memcpy instead of strncpy for dyn_string insertion

[Martin Sebor via Gcc-patches]

Calling strncpy in libiberty's dyn_string_insert() with the last
argument equal to the length of the second triggers the warning:
/src/gcc/master/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);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/src/gcc/master/libiberty/dyn-string.c:272:16: note: length computed here
  272 |   int length = strlen (src);
      |                ^~~~~~~~~~~~

The attached patch avoids the warning by calling memcpy instead.

I'll go ahead and commit the patch as obvious if there are no
concerns/objections.

Martin
libiberty/ChangeLog:

	* dyn-string.c (dyn_string_insert_cstr): Use memcpy instead of strncpy
	to avoid warnings.

diff --git a/libiberty/dyn-string.c b/libiberty/dyn-string.c
index ea711182ca5..8d2456b86c8 100644
--- a/libiberty/dyn-string.c
+++ b/libiberty/dyn-string.c
@@ -277,7 +277,7 @@ dyn_string_insert_cstr (dyn_string_t dest, int pos, const char *src)
   for (i = dest->length; i >= pos; --i)
     dest->s[i + length] = dest->s[i];
   /* Splice in the new stuff.  */
-  strncpy (dest->s + pos, src, length);
+  memcpy (dest->s + pos, src, length);
   /* Compute the new length.  */
   dest->length += length;
   return 1;