libmicrohttpd: bump to version 0.9.57

libmicrohttpd: bump to version 0.9.57

Drop libgcrypt dependency for SSL support; with newer version of gnutls
libgcrypt is not needed.

Drop the LIBS fix for static linking with gnutls that has been
introduced in commit 2d3d6d258bb (libmicrohttpd: fix static linking with
gnutls). gnutls does not support static linking anymore.

Fix a comment typo.

Add license hash.

Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>