Fix [vdso] handling on Android (x86 and aarch64)

* Add in-memory object file handling to the core dynamic loader
* Fix in memory object file handling in ObjectFileELF (previously
  only part of the file was loaded before parsing)
* Fix load address setting in ObjectFileELF for 32-bit targets
  when the load bias is negative
* Change hack in DYLDRendezvous.cpp to be more specific and not to
  interfere with object files with fixed load address

Differential revision: http://reviews.llvm.org/D10800

llvm-svn: 241057