Deprioritize top level -O2 in CMAKE_CXX_FLAGS_RELEASE

[AdrianLundell]

By prepending rather than appending to CMAKE_CXX_FLAGS_RELEASE, it allows to specify another optimization level earlier in the build process and still have that take precedence over the -O2.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

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[zingo]

@digantdesai this changes a global cmake file you might want to test/review this a bit more maybe?

[digantdesai]

I think this is OK. Can we check if "left to right" precedence is generally true beyond gcc, clang, also for msvc for example?

[AdrianLundell]

I think this is OK. Can we check if "left to right" precedence is generally true beyond gcc, clang, also for msvc for example?

This link suggests that it is true for MSVC: https://learn.microsoft.com/en-us/cpp/build/reference/order-of-cl-options?view=msvc-170. Any other important compilers?

A compromise could also be to compile kernels with -O3 and other code with -O2, what do you think about that?

[digantdesai]

I think this is OK. Can we check if "left to right" precedence is generally true beyond gcc, clang, also for msvc for example?

This link suggests that it is true for MSVC: learn.microsoft.com/en-us/cpp/build/reference/order-of-cl-options?view=msvc-170. Any other important compilers?

A compromise could also be to compile kernels with -O3 and other code with -O2, what do you think about that?

Thanks for checking MSVC.

IMO, I guess for a given deployment they should be able to overwrite the default in the CMake.

[zingo]

Got OK to merge from @digantdesai and @swolchok in text form in the commets