Support looping in CrashCatcher_Entry()

If CrachCatcher_DumpEnd() returns CRASH_CATCHER_TRY_AGAIN then the
whole dumping process should cycle again.  This might prove useful
when dumping to something like the UART.  If the user missed logging
the results the first time, they could get a chance to try again.
Fix ARM build errors

Once I started trying to build the core for ARM, I encountered a few
bugs in the code which didn't show up in llvm used for OS X host
builds.
* I forgot to include some standard headers.
* I had to correct some casting so that it would work on 32-bit and
  64-bit architectures.
Makefile now builds core for ARM

The build now generates libCrashCatcher_armv6m.a and
libCrashCatcher_armv7m.a libraries which just contain the core of
CrashCatcher.