[llvm] [PGO] Ensure non-zero entry-count after `populateCounters` (PR #112029)

[Michael O'Farrell via llvm-commits]

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@@ -0,0 +1,28 @@
+; RUN: llvm-profdata merge %S/Inputs/fix_entry_count_sampled.proftext -o %t.profdata
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mofarrell wrote:

These testing oddities were mimicking the approach taken in other nearby tests covering the same functionality.  In particular [fix_entry_count.ll](https://github.com/llvm/llvm-project/blob/main/llvm/test/Transforms/PGOProfile/fix_entry_count.ll) was used as a base.

In `llvm/test/Transforms/PGOProfile/` no other test makes use of split-file for proftext data, does this make it reasonable to follow this localized convention despite the proftext only being used by one test?

https://github.com/llvm/llvm-project/pull/112029