Reduce the number of files probed when finding a lisp file.

Reduce the number of files probed when finding a lisp file.

* src/lread.c (get-load-suffixes): Do not add any suffix to files that
need to be loaded by the dynamic linker.
(effective_load_path): Remove function.
(load): Don't add any suffix if file ends in a suffix already.
(effective_load_path): Remove function.
(openp_add_middle_dir_to_suffixes): Add helper function to create
pairs of middle directories and suffixes.
(openp_max_middledir_and_suffix_len): Add helper function to count the
number of bytes needed to store the middle directory and suffix.
(openp_fill_filename_buffer): Add helper function to copy middle
directory, basename and suffix to the filename buffer.