fuzz: http_request workaround for libevent < 2.1.1

Before libevent 2.1.1, internal functions names didn't end with an underscore.

src/test/fuzz/http_request.cpp

@@ -9,6 +9,7 @@
 #include <test/fuzz/util.h>
 
 #include <event2/buffer.h>
+#include <event2/event.h>
 #include <event2/http.h>
 #include <event2/http_struct.h>
 
@@ -17,8 +18,24 @@
 #include <string>
 #include <vector>
 
+// workaround for libevent versions before 2.1.1,
+// when internal functions didn't have underscores at the end
+#if LIBEVENT_VERSION_NUMBER < 0x02010100
+extern "C" int evhttp_parse_firstline(struct evhttp_request*, struct evbuffer*);
+extern "C" int evhttp_parse_headers(struct evhttp_request*, struct evbuffer*);
+inline int evhttp_parse_firstline_(struct evhttp_request* r, struct evbuffer* b)
+{
+    return evhttp_parse_firstline(r, b);
+}
+inline int evhttp_parse_headers_(struct evhttp_request* r, struct evbuffer* b)
+{
+    return evhttp_parse_headers(r, b);
+}
+#else
 extern "C" int evhttp_parse_firstline_(struct evhttp_request*, struct evbuffer*);
 extern "C" int evhttp_parse_headers_(struct evhttp_request*, struct evbuffer*);
+#endif
+
 std::string RequestMethodString(HTTPRequest::RequestMethod m);
 
 void test_one_input(const std::vector<uint8_t>& buffer)