configure.ac: fixed typo prevented thread naming on FreeBSD
configure.ac: fixed typo prevented thread naming on FreeBSD

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