llvm-dwarfdump: implement --find for .apple_names

llvm-dwarfdump: implement --find for .apple_names

This patch implements the dwarfdump option --find=<name>.  This option
looks for a DIE in the accelerator tables and dumps it if found.  This
initial patch only adds support for .apple_names to keep the review
small, adding the other sections and pubnames support should be
trivial though.

Differential Revision: https://reviews.llvm.org/D38282

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314439 91177308-0d34-0410-b5e6-96231b3b80d8