[3.13] gh-131675: Fix `mi_atomic_yield` in mimalloc on 32-bit ARM (gh-131784) (gh...

[3.13] gh-131675: Fix `mi_atomic_yield` in mimalloc on 32-bit ARM (gh-131784) (gh-131954)

Use the standard `__ARM_ARCH` macro, which is supported by GCC and Clang.

The branching logic for of `__ARMEL__` has been removed so if the target
architecture supports v7+ instructions, a yield is emitted, otherwise a nop
is emitted. This covers both big and little endian scenarios.
(cherry picked from commit 03f6c8e239723637811fd8d278661f5292351197)

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Co-authored-by: Vincent Fazio <vfazio@gmail.com>