Fixing layout of elf-core file related structures

Summary:
The binary layout of prstatus and prpsinfo was wrong.
Some of the member variables where not aligned properly
and others where with a wrong type (e.g. the time related
stuff in prstatus).

I used the structs defined in bfd in binutils to see what the layout
of the elf-core format in these section is.
(https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=bfd/hosts/x86-64linux.h;h=4e420a1f2081dd3b51f5d6b7a8e4093580f5cdb5;hb=master)
Note: those structures are only for x86 64 bit elf-core files

This shouldn't have any impact on the functionality, because
lldb actually uses only a few of the member variables of those structs
and they are with a correct type and alignment.

I found this while trying to add/fix the support for
i386 core files (https://llvm.org/bugs/show_bug.cgi?id=26947)

Reviewers: labath

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D22628
Author: Dimitar Vlahovski <dvlahovski@google.com>

llvm-svn: 276406