STL32 F15x: stm32_stdclockconfig() was calling stm32_pw_setvos() which accessed PWR_CR via an inactive APB. From Juha Niskanen.

Add support for MK20DN--VLH5 and MK20DX---VLH5.  Needed for backward compatible support for Teensy-3.0

SAML21: Since SERCOM5 usese a different output channel, it will also need a different GCLK generator

Add support uClibc++ excpetions.  This involves additional handling for relative relation types, additional support for unwinding, as well as additional changes.  The culmination of a big effort fromo Leo Aloe3132

Basic support for the Kinetis K20 architecture.  Taken from PX4.  This is the work of Jakob Odersky.

SAML21-Xlplained: Add options to enable XOSC32K and to use it as the DFLL source; NSH configure now uses DFLL with OSC16M source