What predefined macro can I use to detect clang?

Found the answer using strings + grep :

$ strings /usr/bin/clang | grep __ | grep -i clang
__clang__

This question has been answered for years but let me add (for future reference) how it is done in Windows:

echo | clang -dM -E -

same as for GCC:

echo | gcc -dM -E -

Please note: The last dash - is actually important! (Otherwise you get error: no input files for both compilers)

To get a list of all the predefined macros that the compiler uses, use this:

clang -dM -E -x c /dev/null

You can do the same for gcc.