Windows uses OSFiber_windows.hpp.
macOS and Linux uses OSFiber_asm_* or OSFiber_ucontext.hpp
Android has no support for makecontext / swapcontext, and so relies on the OSFiber_asm_* implementations.

Unlike makecontext, swapcontext or the Windows fiber APIs, these assembly implementations *do not* save or restore signal masks, floating-point control or status registers, FS and GS segment registers, thread-local storage state nor any SIMD registers.

This should not be a problem as the yarn scheduler requires fibers to be executed on a single thread.

Bug: b/139010488
Change-Id: I5f890ffe4f069361a7eeae64567a77be3a4ba008
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/34771Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>