clang and gcc are not very different from a user's point of view—clang deliberately supports a large number of gcc extensions and command-line options. For that matter, so do other C compilers (e.g. the EDG front-end, used by the intel C compiler).
So really these days "gcc" is as much a common dialect of C as it is a particular compiler.
The book should have the word "GNU" wedged in it.
I'd like to have seen some discussion of llvm/clang as well.