The problem you are seeing is due to two separate issues.  (1) The first time you build Python 3 in a particular build directory, the Abstract Syntax Definition Language (asdl) parser build step may be unnecessarily run by "make" if the time stamps of the source files are not preserved, for example, for an initial clone of a repo using hg.  The parser step requires the use of an existing Python on your system.  It appears you a Python 2.7 installed and first on the your shell $PATH.  Unfortunately, that causes you to run into the second issue, which was documented in Issue9516, a bug in the initial releases of Python 2.7.x.  The fix for that issue is now released in Python 2.7.3, so that the interpreter on OS X is no longer incorrectly checking MACOSX_DEPLOYMENT_TARGET settings.  So, among other solutions, you can either update to Python 2.7.3 or remove it from your PATH during the initial build (until the asdl target is up-to-date).