rework suppress_tinyusb_warnings

* gcc 9.2.1 has some spurious -Wconversion warnings
* cmake 3.18 and above require set_target_properties to be added from the target directory (so added it to all examples)
* fixed a few warnings in a couple of examples

examples/device/cdc_dual_ports/src/main.c

@@ -60,12 +60,12 @@ static void echo_serial_port(uint8_t itf, uint8_t buf[], uint32_t count)
     if (itf == 0)
     {
       // echo back 1st port as lower case
-      if (isupper(buf[i])) buf[i] += 'a' - 'A';
+      if (isupper(buf[i])) buf[i] = (uint8_t) (buf[i] + 'a' - 'A');
     }
     else
     {
       // echo back 2nd port as upper case
-      if (islower(buf[i])) buf[i] -= 'a' - 'A';
+      if (islower(buf[i])) buf[i] = (uint8_t) (buf[i] - 'a' - 'A');
     }
 
     tud_cdc_n_write_char(itf, buf[i]);

examples/device/hid_composite/src/main.c

@@ -230,7 +230,7 @@ void tud_hid_report_complete_cb(uint8_t instance, uint8_t const* report, uint8_t
   (void) instance;
   (void) len;
 
-  uint8_t next_report_id = report[0] + 1;
+  uint8_t next_report_id = (uint8_t)(report[0] + 1);
 
   if (next_report_id < REPORT_ID_COUNT)
   {