Power9 and __builtin_byte_in_range

I'm trying to compile a Power9 program with Clang 7.0:

$ $HOME/llvm/bin/clang++ -mcpu=power9 -maltivec
TestPrograms/test_ppc_power9.cxx:6:11: error: use of undeclared identifier
        bool x = __builtin_byte_in_range(b, r);
1 error generated.

I'm not sure if Clang 7.0 uses another builtin, or if Clang does not
support Power9.

I guess I have one of two questions:

  1. What is LLVM's name for __builtin_byte_in_range?

  2. Which Clang compilers support Power9?