[clang] [PowerPC] Make "ca" aliased to "xer" (PR #77557)

[Qiu Chaofan via cfe-commits]

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@@ -782,6 +782,8 @@ ArrayRef<const char *> PPCTargetInfo::getGCCRegNames() const {
 const TargetInfo::GCCRegAlias PPCTargetInfo::GCCRegAliases[] = {
     // While some of these aliases do map to different registers
     // they still share the same register name.
+    // Strictly speaking, "ca" is a subregister of "xer". However currently we
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ecnelises wrote:

Should be a `FIXME:`?

https://github.com/llvm/llvm-project/pull/77557