[llvm] [AArch64] Disable loop alignment for Windows targets (PR #67894)

[Martin Storsjö via llvm-commits]

================
@@ -1402,6 +1402,9 @@ static void ARM64EmitUnwindInfo(MCStreamer &streamer, WinEH::FrameInfo *info,
     // here, but we'd have to emit the pdata, the xdata header, and the
     // epilogue scopes later, since they depend on whether the we need to
     // split the unwind data.
+    //
+    // If this is fixed, remove code in AArch64ISelLowering.cpp that
----------------
mstorsjo wrote:

This is a large comment block, that starts out with:
```
    // FIXME: GetAbsDifference tries to compute the length of the function
    // immediately, before the whole file is emitted, but in general
    // that's impossible: the size in bytes of certain assembler directives
    // like .align and .fill is not known until the whole file is parsed and
    // relaxations are applied. Currently, GetAbsDifference fails with a fatal
    // error in that case.
```
(And then goes on about potential ways of fixing it.) So this comment says that if this whole general issue/limitation is fixed, we can remove this tweak.

https://github.com/llvm/llvm-project/pull/67894