Bug #11715 - generate header in the build tree.

The module header was being placed in the source tree before. Thanks to
Marcel Loose for the patch, this ensures the file is written to the
build tree.

Modules/FindPythonLibs.cmake

@@ -151,6 +151,7 @@ FUNCTION(PYTHON_WRITE_MODULES_HEADER _filename)
   GET_FILENAME_COMPONENT(_name "${_filename}" NAME)
   STRING(REPLACE "." "_" _name "${_name}")
   STRING(TOUPPER ${_name} _nameUpper)
+  SET(_filename ${CMAKE_CURRENT_BINARY_DIR}/${_filename})
 
   SET(_filenameTmp "${_filename}.in")
   FILE(WRITE ${_filenameTmp} "/*Created by cmake, do not edit, changes will be lost*/\n")