Warning "Use of GNU statement expression extension"

I have this Objective-C istruction:

NSRange range = NSMakeRange(i, MIN(a, b));

where a and bare NSUIntegers.

MIN() is the macro defined in the standard NSObjCRuntime.hheader file as:

#if !defined(MIN)
   #define MIN(A,B) ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a < __b ? __a : __b; })
#endif

During the compilation, the LLVM Compiler 4.1 highlights my instruction showing the warning: "Use of GNU statement expression extension".

What does this mean? Is it my fault? If yes, how can I fix it? If not, how can I remove the compiler warning?