Fix ARM build issues

[uklotzde]

Typo & detection

[Be-ing]

Let's give it a try? 🤷

[uklotzde]

Is the regex reasonable? Inspired from here: https://github.com/opencv/opencv/blob/8c221981bf7e2c8eb87302d70000aa246641487c/cmake/OpenCVDetectCXXCompiler.cmake#L91

The typo is a real bug.

[daschuer]

Probably not.
I have just found this list:
https://stackoverflow.com/questions/45125516/possible-values-for-uname-m
There are no capital versions.

[uklotzde]

Btw, we also use AMD64, but not amd64 which seems to be more common. Out of scope.

[uklotzde]

The conditional processor/architecture dependent stuff is full of redundancies and old cruft. Needs to be rewritten at some time.

[daschuer]

This regex does not work now, because it matches a "armv8b" which is a arm64. This means it matches some arm64.
Please revert to the original and add a comment why this is correct.
Something like:
// CMAKE_SYSTEM_PROCESSOR is just "arm" for all 32 bit ARMs. These flags are not valid with AArch64 and ARMv8 targets where CMAKE_SYSTEM_PROCESSOR is one of ("aarch64_be (arm64)", "aarch64 (arm64)", "armv8b (arm64 compat)" and "armv8l (arm64 compat)".

[uklotzde]

Someone else may take over.

[uklotzde]

Final proposal. I am not doing research on ARM architectures.

[uklotzde]

You may add the comments you think are required later.

[uklotzde]

Btw, STREQUAL "arm" never worked, because otherwise the bug would have been detected.

[daschuer]

Thank you.
You are right, it also has not worked on our PPA. There is a "armv7l" reported.
I am curious if this really helps for your NaN bug.

[uklotzde]

No, it won't fix the NaN issue. This was just a bycatch.