normalize use of stdio functions taking a stream

We should never use stdio functions that use stdout implicitly. Saving a
few characters isn't worth the inconsistency. Too, using the forms such
as `fwprintf()` which take an explicit stream makes it easier to find
the places we write to stdout versus stderr.

Fixes #3728

src/autoload.cpp

@@ -25,7 +25,7 @@
 static const int kAutoloadStalenessInterval = 15;
 
 file_access_attempt_t access_file(const wcstring &path, int mode) {
-    // wprintf(L"Touch %ls\n", path.c_str());
+    // fwprintf(stderr, L"Touch %ls\n", path.c_str());
     file_access_attempt_t result = {};
     struct stat statbuf;
     if (wstat(path, &statbuf)) {