ARM64: use the integrated assembler on ELF.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206378 91177308-0d34-0410-b5e6-96231b3b80d8
ARM64: use 32-bit moves for constants where possible.

If we know that a particular 64-bit constant has all high bits zero, then we
can rely on the fact that 32-bit ARM64 instructions automatically zero out the
high bits of an x-register. This gives the expansion logic less constraints to
satisfy and so sometimes allows it to pick better sequences.

Came up while porting test/CodeGen/AArch64/movw-consts.ll: this will allow a
32-bit MOVN to be used in @test8 soon.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206379 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64/ARM64: port across stub handling for ELF C++ exceptions.

The most important part here is that we should actuall emit the stubs we refer
to in the exception table, but as a side issue this uses more sensible & GCC
compatible representations for some of the bits of information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206380 91177308-0d34-0410-b5e6-96231b3b80d8
AArch64/ARM64: add another set of tests from AArch64

Another batch with no code changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206381 91177308-0d34-0410-b5e6-96231b3b80d8