[clang] [llvm] [BPF] Make -mcpu=v3 as the default (PR #107008)

[via cfe-commits]

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@@ -38,16 +38,22 @@ void BPFTargetInfo::getTargetDefines(const LangOptions &Opts,
 
   Builder.defineMacro("__BPF_FEATURE_ADDR_SPACE_CAST");
 
-  if (CPU.empty() || CPU == "generic" || CPU == "v1") {
+  if (CPU == "generic" || CPU == "v1") {
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eddyz87 wrote:

Nitpick: I think it would be more clear to add a line like below:

```
if (CPU.empty)
  CPU = "v3";
```

(and do the same thing in `BPFSubtarget::initSubtargetFeatures`)

https://github.com/llvm/llvm-project/pull/107008