[dsymutil] Add the ability to run the DWARF verifier on the input

Currently you can run the DWARF verifier on the linked dsymutil output.
This patch extends this functionality and makes it possible to
run the DWARF verifier on the input as well.

A new option --verify-dwarf allows you to specify input, output, all and
none. The existing --verify flag remains unchanged and acts and alias
for --verify-dwarf=output.

Input verification issues do not result in a non-zero exit code because
dsymutil is capable of taking invalid DWARF as input and producing valid
DWARF as output.

Differential revision: https://reviews.llvm.org/D89216