Even though Apple Xcode is based on and similar to Clang,
it does not support the asm goto construct which was added
in commit 668a5f3d (MDEV-26720)
to work around a compiler deficiency that results in suboptimal
code being generated for IA-32 and AMD64.

We will disable this manual optimization if __APPLE_CC__ is defined.

Similar constructs are also used in sync/srw_lock.cc, but that code
is not used on Apple, because we have not implemented a Linux futex
compatible interface on Apple macOS.

Thanks to Valerii Kravchuk for reporting and testing this.