On Windows: Fix compilation against perl 5.18, which somehow thinks that
Visual C++ support gnu's/mingw's __inline__.

* build/generator/gen_win_dependencies.py
  (_find_perl): Add a forced include when using perl 5.18 or later.

* subversion/bindings/swig/perl/libsvn_swig_perl/swigutil_pl.c
  (includes): Include swigutil_pl__pre_perl.h directly.

* subversion/bindings/swig/perl/libsvn_swig_perl/swigutil_pl__pre_perl.h
  New file.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1543980 13f79535-47bb-0310-9956-ffa450edef68