Add support for Darwin’s static library table of contents with 64-bit offsets...

Add support for Darwin’s static library table of contents with 64-bit offsets to the archive members.

Darwin added support in its Xcode 8.0 tools (released in the beta) for static
library table of contents with 64-bit offsets to the archive members.  The
change is very straight forward.  The table of contents member is named
___.SYMDEF_64 or "___.SYMDEF_64 SORTED" and same layout is used but with
fields using 64 bit values instead of 32 bit values.

rdar://26869808

llvm-svn: 273058