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? Take the develo

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? Take the developer DVD that came with your Mac, put it in the drive, and double-click the install icon?