苹果家的 cpp 行为不一致

gistfile1.c

#define a(k) printf("k")

int main() {
  a(hello);
}

gistfile2.txt

$ cpp --version
i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ cpp 1.c
# 1 "1.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "1.c"


int main() {
  printf("hello");
}