Peter,

Your typedefs are outside the conditional sections for C51/AVR.

Presumably, this just happens to work in this case - but, in general, they should be within your compiler-specific sections.

It is also good to specifically test for supported compilers, and have any other give an error; eg

#if defined __C51__
// Keil C51 specific stuff
typedef unsigned char  u8;
typedef   signed char  s8;
typedef unsigned short u16;
typedef   signed short s16;
typedef unsigned long  u32;
typedef   signed long  s32;

#elif defined __GNUC__
// GCC-AVR specific stuff
typedef unsigned char  u8;
typedef   signed char  s8;
typedef unsigned short u16;
typedef   signed short s16;
typedef unsigned long  u32;
typedef   signed long  s32;

#else
// Neither GCC nor C51 - force the user to take specifc action!
#error Unsupported Compiler!

#endif