[Ada] Fix PR ada/82813

[Eric Botcazou]

-Wstringop-overflow is supposed to be a C-family warning but it is somehow 
issued in Ada too and can warn on bogus cases so let's just kill it.

Tested on x86-64/Linux, applied on the mainline and 7 branch.


2018-03-12  Eric Botcazou  <ebotca...@adacore.com>

        PR ada/82813
        * gcc-interface/misc.c (gnat_post_options): Disable string overflow
        warnings.

-- 
Eric Botcazou
Index: gcc-interface/misc.c
===================================================================
--- gcc-interface/misc.c	(revision 258411)
+++ gcc-interface/misc.c	(working copy)
@@ -265,6 +265,9 @@ gnat_post_options (const char **pfilenam
   /* No return type warnings for Ada.  */
   warn_return_type = 0;
 
+  /* No string overflow warnings for Ada.  */
+  warn_stringop_overflow = 0;
+
   /* No caret by default for Ada.  */
   if (!global_options_set.x_flag_diagnostics_show_caret)
     global_dc->show_caret = false;