ctypes-ptyon: Use the CPP detected as part of our configure run rather than
the CPP detected when APR was built.

This fixes building ctypes-python on newer versions of OS X (>= 10.8).  APR
was built with CC=`xcrun --find cc`.  However, that path is dependent upon
the version of Xcode installed, as a result the output of `apr-config --cpp`
may point to a non-existant path.

* Makefile.in
  (CPP): Set a variable we already have been bothering to detect.
  (ctypes-pathon): Pass the CPP variable into the run_ctypesgen.sh script.

* run_ctypesgen.sh
  (cpp): Set from command line argument rather than from apr-config.




git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1536537 13f79535-47bb-0310-9956-ffa450edef68