[BUG]: -flto=thin from CMAKE_INTERPROCEDURAL_OPTIMIZATION_CONFIG is not respected

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What version (or hash if on master) of pybind11 are you using?

f33f6afb667b6b5c0da7dee98dc02f51b4cc0e96

Problem description

I want to enable lto in Release mode only. I added set(CMAKE_INTERPROCEDURAL_OPTIMIZATION_RELEASE TRUE) in my CMakeLists.txt.

Since I didn't set CMAKE_INTERPROCEDURAL_OPTIMIZATION, line https://github.com/pybind/pybind11/blob/f33f6afb667b6b5c0da7dee98dc02f51b4cc0e96/tools/pybind11Common.cmake#L397 think I didn't already enabled -flto=thin and add -flto. So when building in Release mode, I have : -flto=thin -flto.

I bypass the problem by setting THIN_LTO in pybind11_add_module.

Reproducible example code

No response

Is this a regression? Put the last known working version here if it is.

Not a regression

Read tools/pybind11Common.cmake around line 397, then configure a Release build with CMAKE_INTERPROCEDURAL_OPTIMIZATION_RELEASE enabled and inspect the generated flags. Done means the configuration respects the requested ThinLTO setting without adding a duplicate or conflicting -flto option.