[compiler-rt] asan_static x86-64: Support 64-bit ASAN_SHADOW_OFFSET_CONST redux (PR #76185)

[Dan McGregor via llvm-commits]

dankm wrote:

I think @MaskRay should probably verify this. I'm not 100% on my x86 assembly.

https://github.com/llvm/llvm-project/pull/76185