How to fix "expected '=', ',', ';', 'asm' or '__attribute__' before 'ioctl' " error ?

You are probably using gcc which complains about __cdecl which is compiler and processor specific. If your embedded system does not use a x86 CPU you may use an empty global definition to hide it:

#define __cdecl

However, there may be other issues coming up so you should check if you can setup your development environment for your target platform.

With x86 CPUs, gcc uses __attribute__ to specify the C calling convention and you can use:

#define __cdecl __attribute__((__cdecl__))

For further questions you should provide additional information about the used compiler (name and version) and target platform (architecture and OS).