AArch64: implement large code model access to global variables.

The MOVZ/MOVK instruction sequence may not be the most efficient (a
literal-pool load could be better) but adding that would require
reinstating the ConstantIslands pass.

For now the sequence is correct, and that's enough. Beware, as of
commit GNU ld does not appear to support the relocations needed for
this. Its primary purpose (for now) will be to support JITed code,
since in that case there is no guarantee of where your code will end
up in memory relative to external symbols it references.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181117 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64: implement support for blockaddress in large code model

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181118 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64: support large code model for jump-tables

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181119 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64: support literal pool access in large memory model.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181120 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64: assert code model is small for TLS accesses

Supporting TLS in the large memory model is rather difficult at the
moment, so make sure no-one gets into difficulties by mistake.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181121 91177308-0d34-0410-b5e6-96231b3b80d8