Changes for Bug 17384

Summary:
Virtual dynamic shared objects, or vdso files were 
not loaded for Linux OS.In Bug 17384 the call 
stack could not be unwinded from functions
residing in the vdso object.

This commit adds support for loading such files by
reading the Aux vectors since a vdso is invisibily 
mapped to the inferiors address space and the
 actual file is not present in the filesystem. The 
presence of the vdso is detected by inspecting 
the Aux vector for AT_SYSINFO_EHDR tag.

Reviewers: lldb-commits, ovyalov, tberghammer

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D14118

llvm-svn: 251505