What's a good way to check availability of __restrict keyword?

Question

I am looking a set of #ifdef's to check availability of __restrict keyword for GCC and Visual Studio. I assume that it needs to check compiler version, but I don't know for which versions it was introduced. Anyone that can help me out?

UPDATE: This must (and only needs to) work when compiling as C89! So I cannot rely on __STDC_VERSION__ indicating C99, or C99 support.