Libmicrohttpd works nicely without https support, so make it optional.
Also ensure the cross-libgcrypt-config is found, rather than whatever
is installed on the host.
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
libmicrohttpd is a library that allows embedding an HTTP server into
an application with a small code and memory footprint.
Signed-off-by: Will Newton <will.newton@gmail.com>
