Correct x86_64 Android fp128 mangled name

These changes are for Android x86_64 targets to be compatible with current Android g++.
https://llvm.org/bugs/show_bug.cgi?id=23897
Use 'g' and 'Cg' for "long double" and "long double _Complex" mangled type names.

Differential Revision: http://reviews.llvm.org/D11466

llvm-svn: 243133