Wrong macro for the Clang version

[intractabilis]

https://github.com/tzlaine/parser/blob/4cea9c03d6baf8165a21162e66be4f99ec85b529/include/boost/parser/config.hpp#L83 __clang__ above is not the Clang version; it's equal to 1.

$ clang++ --version
clang version 18.1.4 (https://github.com/llvm/llvm-project.git e6c3289804a67ea0bb6a86fadbe454dd93b8d855)
Target: x86_64-unknown-linux-gnu
Thread model: posix
$ clang++ -x c++ -E -dD - < /dev/null 2>&1 | grep __clang__
#define __clang__ 1

You probably meant __clang_major__:

$ clang++ -x c++ -E -dD - < /dev/null 2>&1 | grep __clang_major__
#define __clang_major__ 18