fsearch: write only found files to stdout and use implicit file offset

In the emper-fs-eval I would like to validate the output of the fsearch
variants against a list of known files. Not writing any log messages to
stdout make that easier.

Use -1 as the offset of the write to stdout.
Passing offset -1 means to use the file's implicit offset just like write(2).
When using a tty as stdout offset 0 is fine but when redirecting stdout
to a file 0 will cause that previously found paths will always be
overwritten.

apps/fsearch/fsearch.cpp

@@ -51,7 +51,7 @@ void search(const std::string& path) {
 			std::array<char, PATH_MAX + 1> outBuf;
 			memcpy(outBuf.data(), path.c_str(), path.length());
 			outBuf[path.length()] = '\n';
-			emper::io::writeFileAndWait(STDOUT_FILENO, outBuf.data(), path.length() + 1, 0);
+			emper::io::writeFileAndWait(STDOUT_FILENO, outBuf.data(), path.length() + 1, -1);
 			goto out;
 		}
 
@@ -105,9 +105,9 @@ static auto fssearch(const po::variables_map& vm) -> int {
 
 	Runtime runtime;
 
-	std::cout << "Starting fsearch with stealingMode=" << stealingMode;
-	if (max_running) std::cout << " and " << max_running->getCount() << " file fibers";
-	std::cout << std::endl;
+	std::cerr << "Starting fsearch with stealingMode=" << stealingMode;
+	if (max_running) std::cerr << " and " << max_running->getCount() << " file fibers";
+	std::cerr << std::endl;
 
 	auto* dirWalker = Fiber::from(walk_dir);
 	runtime.scheduleFromAnywhere(*dirWalker);