Fix the libc++ pretty printers for the android NDK

The libc++ shipped with the android NDK is shipped using a different
internal namespace then the upstream libc++ (__ndk1 vs. __1) to avoid
an ODR violation between the platform and the user application. This
change fixes our pretty printers to be able to work with the types
from the android NDK libc++.

Differential revision: http://reviews.llvm.org/D21680

llvm-svn: 274489