Fix: Inaccurate mangled names.

1) + Minor code cleanup.

Test: header-abi-dumper -o example1.dump tests/input/example1.cpp -I tests --
-x c++ -std=c++11 -I . -I ~/android/aosp/external/clang/lib/Headers.
Inspected example1.dump. It doesn't contain mangled names of the form
"name_mangled_name"  anymore.

Bug: 36871006

Change-Id: I3a12ae36d59e1db6db473532d10c36b1f77861ef