determinize: various micro optimizations

* spot/twaalgos/determinize.cc: Implement various micro
optimizations.  Use robin-hood hashing in a few places.
* spot/priv/robin_hood.hh: New file.
* spot/priv/Makefile.am: Add it.
* tests/sanity/80columns.test, tests/sanity/includes.test,
tests/sanity/style.test: Adjust to skip robin_hood.hh.

tests/sanity/style.test

@@ -68,6 +68,7 @@ for dir in "$TOP/spot" "$TOP/bin" "$TOP/tests"; do
                  -a -type f -a -print |
   while read file; do
     if $GREP 'GNU Bison' "$file" >/dev/null ||
+      $GREP '/robin-hood-hashing' "$file" >/dev/null ||
       $GREP 'generated by flex' "$file" >/dev/null ; then
       continue
     fi