mhd_threads.h: Fixed typo in macro.
mhd_threads.h: Fixed typo in macro.

maru/libmicrohttpd-http2,ghaderer/libmicrohttpd,maru/libmicrohttpd-http2,ghaderer/libmicrohttpd,ghaderer/libmicrohttpd,maru/libmicrohttpd-http2