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

[bansan85]

Required prerequisites

• [X] Make sure you've read the documentation. Your issue may be addressed there.
• [X] Search the issue tracker and Discussions to verify that this hasn't already been reported. +1 or comment there if it has.
• [ ] Consider asking first in the Gitter chat room or in a Discussion.

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