[BUG]: Invalid flag unnecessarily forces FLTO test to fail with gcc on macOS

[barracuda156]

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

3.0.3

Problem description

-fno-fat-lto-objects may not to be supported by gcc on macOS, and FLTO test fails, unnecessarily so, since gcc does support -flto and flto=auto. The problem originates from

pybind11/tools/pybind11Common.cmake

Lines 355 to 356 in 00a9c62

	elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU" AND NOT MINGW)
	set(cxx_append ";-fno-fat-lto-objects")

Reproducible example code

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

Not a regression