Fix for Bug 25338

Summary:
The issue arises because LLDB is not
able to read the vdso library correctly.
The fix adds memory allocation callbacks
to allocate sufficient memory in case the
requested offsets don't fit in the memory
buffer allocated for the ELF.

Reviewers: lldb-commits, clayborg, deepak2427, ovyalov, labath, tberghammer

Differential Revision: http://reviews.llvm.org/D16107

llvm-svn: 258122