This adds support for the 64-bit DWARF format, but is still limited to
less than 4GB of debug data by the DataExtractor class. Some versions
of the GNU MIPS toolchain generate 64-Bit DWARF even though it isn't
actually necessary.
Differential Revision: http://reviews.llvm.org/D1988
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238434 91177308-0d34-0410-b5e6-96231b3b80d8
