[llvm] r262388 - Revert "[AArch64] Fix isLegalAddImmediate() to return true for valid negative values."

[Tim Northover via llvm-commits]

>     Revert r262248 in an attempt to fix the clang-native-aarch64-full bot

Looks like it's probably got UB for INT64_MIN, though I obviously
don't know if that's actually what's causing the issue.

Tim.