ARM IAS: support .personalityindex

The .personalityindex directive is equivalent to the .personality directive with
the ARM EABI personality with the specific index (0, 1, 2).  Both of these
directives indicate personality routines, so enhance the personality directive
handling to take into account personalityindex.

Bonus fix: flush the UnwindContext at the beginning of a new function.
ARM IAS: improve .eabi_attribute handling

Parse tag names as well as expressions.  The former is part of the
specification, the latter is for improved compatibility with the GNU assembler.
Fix attribute value handling to be comformant to the specification.
ARMAsmParser: fix typo in comment
ARM ELF Streamer: print out tag names

If using verbose asm, print out the friendly name of the tag if possible.