AK: Always use serenity's math routines, even in lagom builds

[nico]

Some of the functions in AK/Math.h used to implement math routines if AK_OS_SERENITY was defined, but called __builtin_foo() in lagom builds.

This was not done consistently. Many functions always implemented math functions without this check, for example:

• copysign()
• acos(), asin()
• cosh(), sinh(), tanh(), acosh, asinh(), atanh()
• exp2(), log2(), pow()

Move the functions that did that check to not doing it as well. This means these functions now use the same implementation in serenity and lagom. Since lagom is for testing serenity code outside serenity, this seems like a good change.

All these functions check for x86 for and use inline assembly there, so this only affects non-x86 lagom builds. It affects these functions:

• fmod()
• remainder() (now always a TODO(), not just in serenity)
• sin(), cos(), tan()
• atan(), atan2()
• log(), log10()

It changes but does not really affect sqrt() -- now a TODO() on non-x86 non-arm non-riscv lagom (i.e. nowhere).

As Serenity's implementations of these math functions are currently lower-quality than what's usually in lagom libms, this regresses lagom behavior (performance, precision) on non-x86 for these functions. But only to the level they're at within serenity, and we'll have to improve these functions there anyways.

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Assuming CI likes this, it'll make it easier to work on #25934 in lagom builds. And it reduces config matrix size for the math routines.

[nico]

This is now down to 16 different LibWeb baselines (from 32 different baselines, and TestComplex failing). Maybe fine to just rebaseline; the diffs look benign (…and we presumably get that output in serenity too).

[spholz]

This is now down to 16 different LibWeb baselines (from 32 different baselines, and TestComplex failing). Maybe fine to just rebaseline; the diffs look benign (…and we presumably get that output in serenity too).

This will break with x86's more accurate inline asm impls though, which are used in lagom and don't fail CI.