Cross Platform (OSX/iOS): Do not redefine uintptr_t for __APPLE__
Cross Platform (OSX/iOS): Do not redefine uintptr_t for __APPLE__

Considering `PAL_STDCPP_COMPAT` is defined;

`uintptr_t` is builtin supported type for OSX/iOS. When
`PAL_STDCPP_COMPAT` is set and without BIT64 (ARM, x86?), `uintptr_t`
was defined as `unsigned int`. However it should be `unsigned long` for
OSX/iOS/WatchOS regardless from arch.

 In order to prevent the accidents in future, a separate
`static_assert` added.

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