Add ARMV6-M support for Cortex-M0 parts

Adding a ARMv6-M version of HardFault_Handler to prepare for entry
into CrashCatcher_Entry().

Changes to the CrashingApp sample include:
* Build for the LPC11U24 version of mbed as well.
* Update main.cpp's implementation of CrashCatcher_GetMemoryRegions()
  to return a different set of RAM memory ranges for the LPC11U24.
* Rewrote test.S in ARMv6-M assembly language so that it would work on
  all of the Cortex-M devices.