Fixing -Werror=format-overflow errors (found by gcc-8.3.1)

sql/sp_head.cc

@@ -2885,7 +2885,7 @@ sp_head::show_routine_code(THD *thd)
       const char *format= "Instruction at position %u has m_ip=%u";
       char tmp[sizeof(format) + 2*SP_INSTR_UINT_MAXLEN + 1];
 
-      sprintf(tmp, format, ip, i->m_ip);
+      my_snprintf(tmp, sizeof(tmp), format, ip, i->m_ip);
       /*
         Since this is for debugging purposes only, we don't bother to
         introduce a special error code for it.

storage/maria/ma_test3.c

@@ -362,7 +362,7 @@ int test_write(MARIA_HA *file,int id,int lock_type)
       maria_extra(file,HA_EXTRA_WRITE_CACHE,0);
   }
 
-  sprintf((char*) record.id,"%7ld", (long) getpid());
+  my_snprintf((char*) record.id, sizeof(record.id), "%7ld", (long) getpid());
   strnmov((char*) record.text,"Testing...", sizeof(record.text));
 
   tries=(uint) rnd(100)+10;

storage/maria/maria_chk.c

@@ -1699,8 +1699,8 @@ static void descript(HA_CHECK *param, register MARIA_HA *info, char *name)
 	null_bit[0]=null_pos[0]=0;
 	if (keyseg->null_bit)
 	{
-	  sprintf(null_bit,"%d",keyseg->null_bit);
-	  sprintf(null_pos,"%ld",(long) keyseg->null_pos+1);
+	  my_snprintf(null_bit, sizeof(null_bit), "%d", keyseg->null_bit);
+	  my_snprintf(null_pos, sizeof(null_pos), "%ld", (long) keyseg->null_pos+1);
 	}
 	printf("%-7ld%-5d%-9s%-10s%-30s\n",
 	       (long) keyseg->start+1,keyseg->length,

storage/myisam/mi_test3.c

@@ -364,7 +364,7 @@ int test_write(MI_INFO *file,int id,int lock_type)
       mi_extra(file,HA_EXTRA_WRITE_CACHE,0);
   }
 
-  sprintf((char*) record.id,"%7ld",(long) getpid());
+  my_snprintf((char*) record.id, sizeof(record.id), "%7ld", (long) getpid());
   strnmov((char*) record.text,"Testing...", sizeof(record.text));
 
   tries=(uint) rnd(100)+10;

storage/myisam/myisamchk.c

@@ -1404,8 +1404,8 @@ static void descript(HA_CHECK *param, register MI_INFO *info, char * name)
 	null_bit[0]=null_pos[0]=0;
 	if (keyseg->null_bit)
 	{
-	  sprintf(null_bit,"%d",keyseg->null_bit);
-	  sprintf(null_pos,"%ld",(long) keyseg->null_pos+1);
+	  my_snprintf(null_bit, sizeof(null_bit), "%d", keyseg->null_bit);
+	  my_snprintf(null_pos, sizeof(null_pos), "%ld", (long) keyseg->null_pos+1);
 	}
 	printf("%-7ld%-5d%-9s%-10s%-30s\n",
 	       (long) keyseg->start+1,keyseg->length,