(Hopefully) fix C++ constructors

teensy4/imxrt.ld

 		KEEP(*(.startup))
 		*(.progmem*)
                 . = ALIGN(4);
-/*
-		TODO: how much of this C++ stuff is really needed?
                 KEEP(*(.init))
-                . = ALIGN(4);
                 __preinit_array_start = .;
                 KEEP (*(.preinit_array))
                 __preinit_array_end = .;
                 __init_array_start = .;
-                KEEP (*(SORT(.init_array.*)))
                 KEEP (*(.init_array))
                 __init_array_end = .;
-*/
 		. = ALIGN(16);
 	} > FLASH
 

teensy4/startup.c

 	printf("AHB divisor = %u\n", ((cbcdr >> 10) & 7) + 1);
 	printf("IPG divisor = %u\n", ((cbcdr >> 8) & 3) + 1);
 
-	// TODO: wait at least 20ms before starting USB
+	while (millis() < 20) ; // wait at least 20ms before starting USB
 	usb_init();
 	analog_init();
 	pwm_init();
 
-	// TODO: wait tat least 300ms before calling setup
+	while (millis() < 300) ; // wait at least 300ms before calling user code
+	printf("before C++ constructors\n");
+	__libc_init_array();
+	printf("after C++ constructors\n");
 	printf("before setup\n");
 	setup();
 	printf("after setup\n");