The Xcode Developer Tools installer also installs the standard system development tools and interfaces into /usr, so conventional makefile- and config-based builds will operate correctly. There is no way to switch among versions of most these tools; the last installed version replaces all other versions. A few of these tools, including /usr/bin/xcodebuild, can switch among versions; see the xcode-select manpage for more information. Installation of these tools can be disabled by turning off the UNIX Development Support choice in the installer.
If the UNIX Development Support is not installed, all projects must build against an SDK, and conventional makefile-based builds should execute the standard development tools from the developer directory’s usr/bin directory instead of the root system’s /usr/bin. This can be done by adding the full path to that directory to the PATH environment variable and making sure that your build scripts and makefiles do not have absolute references to tools such as /usr/bin/gcc, instead always using the shell’s path mechanism to launch the tools. Alternatively, tools can be invoked using a path returned by xcode-select -print-path; see the xcode-selectmanpage for more information.
