When building for Windows x86, we do not have `__i686__` defined, but do
have `__i386__` defined. Ensure that the routines are included for the
x86 Windows target.
Android NDK <r21 does not provide the AEABI mandated `__aeabi_d2h`
functions in the compiler runtime. Add shims to ensure that the
functions are available for building the standard library.