[teensy4] Rename USB sources from .c to .cpp to enable C++ features

[forderud]

Build errors:

• error: 'usb_string_manufacturer_name' aliased to undefined symbol 'usb_string_manufacturer_name_default'
• error: 'usb_string_product_name' aliased to undefined symbol 'usb_string_product_name_default'
• error: 'yield' was not declared in this scope
• error: 'millis' was not declared in this scope

Full build log:

C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_desc.cpp:2722:44: error: 'usb_string_manufacturer_name' aliased to undefined symbol 'usb_string_manufacturer_name_default'
 2722 | extern struct usb_string_descriptor_struct usb_string_manufacturer_name
      |                                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_desc.cpp:2724:44: error: 'usb_string_product_name' aliased to undefined symbol 'usb_string_product_name_default'
 2724 | extern struct usb_string_descriptor_struct usb_string_product_name
      |                                            ^~~~~~~~~~~~~~~~~~~~~~~
In file included from C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb.cpp:4:
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'void usb_serial_class::begin(long int)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:93:25: error: 'yield' was not declared in this scope
   93 |                         yield();
      |                         ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'usb_serial_class::operator bool()':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:167:17: error: 'yield' was not declared in this scope
  167 |                 yield();
      |                 ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'size_t usb_serial_class::readBytes(char*, size_t)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:177:45: error: 'millis' was not declared in this scope
  177 |                 unsigned long startMillis = millis();
      |                                             ^~~~~~
In file included from C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.cpp:32:
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'void usb_serial_class::begin(long int)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:93:25: error: 'yield' was not declared in this scope
   93 |                         yield();
      |                         ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'usb_serial_class::operator bool()':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:167:17: error: 'yield' was not declared in this scope
  167 |                 yield();
      |                 ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'size_t usb_serial_class::readBytes(char*, size_t)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:177:45: error: 'millis' was not declared in this scope
  177 |                 unsigned long startMillis = millis();
      |                                             ^~~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.cpp: In function 'void rx_event(transfer_t*)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.cpp:157:33: warning: comparison of integer expressions of different signedness: 'int' and 'long unsigned int' [-Wsign-compare]
  157 |                         if (len <= CDC_RX_SIZE_480 - count) {
      |                             ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial2.cpp:32:
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'void usb_serial_class::begin(long int)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:93:25: error: 'yield' was not declared in this scope
   93 |                         yield();
      |                         ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'usb_serial_class::operator bool()':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:167:17: error: 'yield' was not declared in this scope
  167 |                 yield();
      |                 ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'size_t usb_serial_class::readBytes(char*, size_t)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:177:45: error: 'millis' was not declared in this scope
  177 |                 unsigned long startMillis = millis();
      |                                             ^~~~~~
In file included from C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial3.cpp:32:
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'void usb_serial_class::begin(long int)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:93:25: error: 'yield' was not declared in this scope
   93 |                         yield();
      |                         ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'usb_serial_class::operator bool()':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:167:17: error: 'yield' was not declared in this scope
  167 |                 yield();
      |                 ^~~~~
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h: In member function 'size_t usb_serial_class::readBytes(char*, size_t)':
C:\Users\100030120\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\cores\teensy4\usb_serial.h:177:45: error: 'millis' was not declared in this scope
  177 |                 unsigned long startMillis = millis();
      |                                             ^~~~~~

exit status 1

Compilation error: exit status 1

[forderud]

Moved to PaulStoffregen#763