Assuming a just-bought vanilla Mac computer, how is someone supposed to install a tarball of GCC or LLVM/Clang sourcecode without a C compiler?

Keep in mind that OS X does not come with "make", "ld", "as", "nasm", "yasm", "gcc", "g++", "cc", "c++", or any others I may have missed.

I understand someone else could provide a pre-compiled package of GCC or Clang for the community, but that is not what the author is talking about in that point. He is specifically talking about end-users and developers of other languages besides C and Objective-C that may require installing packages that need to have native C extensions compiled. ruby-mysql comes to mind, as well as RVM, the Ruby Version Manager, becoming effectively useless without those Ruby developers being forced to buy Xcode, not for Xcode, but for GCC.