also check for curl/curl.h header presence when checking for libcurl
also check for curl/curl.h header presence when checking for libcurl

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