Including every OS' own built-in byte swapping functions is kind of
undesirable, since it adds yet another build path to ensure compilation
succeeds on.
Given we only support clang, GCC, and MSVC for the time being, we can
utilize their built-in functions directly instead of going through the
OS's API functions.
This shrinks the overall code down to just
if (msvc)
use msvc's functions
else if (clang or gcc)
use clang/gcc's builtins
else
use the slow path
This is compromise for swap type being used in union. A union has deleted default constructor if it has at least one variant member with non-trivial default constructor, and no variant member of T has a default member initializer. In the use case of Bitfield, all variant members will be the swap type on endianness mismatch, which would all have non-trivial default constructor if default value is specified, and non of them can have member initializer
swap{16,32,64} are defined as macros on the two, but client code
tries to invoke them as Common::swap{16,32,64}, which naturally
doesn't work. This hack redefines the macros as inline functions
in the Common namespace: the bodies of the functions are the
same as the original macros, but relying on OS-specific
implementation details like this is of course brittle.
Also gets rid of pointer data variants as this prevents the use of
the regular swapping routines as unary predicates in std lib functions.
They also cast to stricter alignment types, which is undefined behavior.
Symbian, Xbox, Blackberry and iOS got removed.
FreeBSD and Android kept due to them potentially being able to run Citra in the future.
The iOS specific part also got removed from PPSSPP in order to fix a bug there.
