Add a new MachineJumpTableInfo entry type, EK_GPRel64BlockAddress, which is

Add a new MachineJumpTableInfo entry type, EK_GPRel64BlockAddress, which is
needed to emit a 64-bit gp-relative relocation entry. Make changes necessary
for emitting jump tables which have entries with directive .gpdword. This patch
does not implement the parts needed for direct object emission or JIT.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@149668 91177308-0d34-0410-b5e6-96231b3b80d8