CI-unixish.yml: added profile-guided optimization (PGO) to callgrind step

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No description provided.

[firewave]

This is to test the impact on performance and to have a foundation to write documentation for the Cppcheck CI/performance guide.

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g++ - 73,362,451 -> 64,757,385
g++ (system) - 1,193,552,892 -> 1,024,590,246
clang++ - 69,009,338 -> 62,589,273
clang++ (system) - 1,258,982,751 -> 1,140,735,791

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Also just like #577 it will highlight things the compiler is able to optimize and should probably not be hand tuned.

[danmar]

what is the difference for g++ and g++ (system) ?

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what is the difference for g++ and g++ (system) ?

That is the selfcheck without and with system includes made available.