internal_rev_object.hpp: do not use __fastcall for non-Windows platforms

[luadebug]

The problem is with the __fastcall calling convention syntax on non-MSVC compilers. The __fastcall is a Microsoft-specific calling convention that's not recognized by GCC/Clang.

/github/home/.xmake/packages/o/omath/v3.9.0/8998370ec7d64573a093ffd40b339792/include/omath/rev_eng/internal_rev_object.hpp:32:49: error: expected ‘;’ before ‘(’ token [-Wtemplate-body]
32 | using VirtualMethodType = ReturnType(__fastcall*)(void*, decltype(arg_list)...);
| ^
/github/home/.xmake/packages/o/omath/v3.9.0/8998370ec7d64573a093ffd40b339792/include/omath/rev_eng/internal_rev_object.hpp:34:39: error: ‘VirtualMethodType’ does not name a type [-Wtemplate-body]
34 | return (reinterpret_cast<VirtualMethodType**>(this))[id](this, arg_list...);
| ^~~~~~~~~~~~~~~~~
/github/home/.xmake/packages/o/omath/v3.9.0/8998370ec7d64573a093ffd40b339792/include/omath/rev_eng/internal_rev_object.hpp:34:56: error: expected ‘>’ before ‘’ token [-Wtemplate-body]
34 | return (*reinterpret_cast<VirtualMethodType**>(this))[id](this, arg_list...);
| ^

microsoft/vcpkg#47731
xmake-io/xmake-repo#8349