[llvm] [nfc] Improve testability of PGOInstrumentationGen (PR #104490)

[Snehasish Kumar via llvm-commits]

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@@ -53,15 +53,18 @@ class PGOInstrumentationGenCreateVar
   bool ProfileSampling;
 };
 
+enum class PGOInstrumentationType { Invalid = 0, FDO, CSFDO, CTXPROF };
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snehasish wrote:

I think the enum members should have a prefix based on guideline here: https://llvm.org/docs/CodingStandards.html#the-low-level-issues

Also camel case (though FDO is an acronym so I'm not sure). 

https://github.com/llvm/llvm-project/pull/104490