Consistent use of anonymous namespace

Also change `bindThisThread` to match the current code style for function naming.

closes https://github.com/official-stockfish/Stockfish/pull/5118

No functional change

src/misc.cpp

@@ -596,14 +596,15 @@ namespace WinProcGroup {
 
 #ifndef _WIN32
 
-void bindThisThread(size_t) {}
+void bind_this_thread(size_t) {}
 
 #else
 
+namespace {
 // Retrieves logical processor information using Windows-specific
 // API and returns the best node id for the thread with index idx. Original
 // code from Texel by Peter Österlund.
-static int best_node(size_t idx) {
+int best_node(size_t idx) {
 
     int   threads      = 0;
     int   nodes        = 0;
@@ -668,10 +669,11 @@ static int best_node(size_t idx) {
     // then return -1 and let the OS to decide what to do.
     return idx < groups.size() ? groups[idx] : -1;
 }
+}
 
 
 // Sets the group affinity of the current thread
-void bindThisThread(size_t idx) {
+void bind_this_thread(size_t idx) {
 
     // Use only local variables to be thread-safe
     int node = best_node(idx);