Speedup Makefile on Windows
The Makefile is notoriously slow on windows, because of new processes
being spawned I believe. This pr improves it a little bit for the help
and config-sanity targets, with the latter also improving `make -j
build` because it depends on that. On the same machine ubuntu (wsl) is
more than 3 times faster, if there are other improvements we can make
I'd be happy to hear about them. Ultimately
https://github.com/official-stockfish/Stockfish/pull/5543 also aims to
improve this I believe, but it will take some additional time before
that lands.
```
make config-sanity:
patch: 6.199s
master: 12.738s
make help:
patch: 3.1s
master: 11.49s
make -j build:
patch: 36s
master: 43.25s
make -j build:
master ubuntu: 10s
```
closes https://github.com/official-stockfish/Stockfish/pull/5642
No functional change