I\'ve just upgraded to Xcode 5 beta with the April 15 2013 commandline tools and hit the following warning when running a cmake build during the standard CMakeTestCCompiler.
run this comment on your client.app:
export PATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:$PATH