[llvm] [PowerPC] Support local-dynamic TLS relocation on AIX (PR #66316)

[Amy Kwan via llvm-commits]

================
@@ -145,9 +163,88 @@ namespace {
                                                               .addImm(0);
 
         if (IsAIX) {
-          // The variable offset and region handle are copied in r4 and r3. The
-          // copies are followed by GETtlsADDR32AIX/GETtlsADDR64AIX.
-          if (!IsTLSTPRelMI) {
+          if (IsTLSLDAIXMI) {
+            // It is better to put TLSLDAIX node before LoadOffsetToc node,
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amy-kwan wrote:

```suggestion
            // It is better to put the TLSLDAIX/TLSLDAIX8 nodes before the node that loads from the TOC (LoadOffsetToc),
```
Maybe it may be good to elaborate just a bit more on the node (something along these lines?)

https://github.com/llvm/llvm-project/pull/66316