Add support for Newlib as an OS/ABI. The only thing that is specific to it
relatively to "generic" baremetal target is location of PC register in jump
buffer for longjump support.
Sniffer uses .ivt section to decide if ELF file is for ARC Newlib or not.
gdb/ChangeLog:
* arc-newlib-tdep.c: New file.
* configure.tgt: Add newlib support for ARC.
Anton Kolesov