Fix build on FreeBSD after r196141

This should probably be replaced with build infrastructure support for
a platform-specific canonical Python include path, but for now it should
restore the FreeBSD buildbot.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@196167 91177308-0d34-0410-b5e6-96231b3b80d8