Thanks, Ronald.  Version 3 addresses various issues, including adding a search of $PATH for clang since xcrun is not useful in the case where the user has installed a standalone Command Line Tools package or has installed a Command Line Tools component from within Xcode but hasn't run xcode-select.  Another problem: the SDK path is likely going to be incorrect in the common case of an installer build on 10.5 or 10.6 but run on 10.7 or later.  It's tricky to get all the edge cases correct for that.  For now, the solution is to delete -sdkroot parameters from the default CFLAGS and friends if the SDK path is invalid; that assumes the Command Line Tools component/package has been installed.  If necessary, the user can override via env variables.  Also, the compiler validity checks are now bypassed if the user has overridden CC.  I'll plan to commit later today for 3.3.0b1 along with some README updates.