* Disable x87 control word for non-x86 targets
On msvc, x87 control word is only available on x86 target. Need to disable it for other targets to prevent compiling problems.
* Include immintrin.h on x86 and x64 only
Immintrin.h is only available on x86 and x64. Need to disable it for other targets to prevent compiling problems.
* All internal header files now require Py_BUILD_CORE or
Py_BUILD_CORE_BUILTIN to be defined.
* _json.c is now compiled with Py_BUILD_CORE_BUILTIN to access
pycore_accu.h header.
* Add an example to Modules/Setup to show how to build _json
as a built-in module; it requires non trivial compiler options.