Use stdlib 'hardware_concurrency' to get logical processor count

This has the benifit of being multiplatform.

src/xenia/base/threading.cc

@@ -12,6 +12,14 @@
 namespace xe {
 namespace threading {
 
+uint32_t logical_processor_count() {
+  static uint32_t value = 0;
+  if (!value) {
+    value = std::thread::hardware_concurrency();
+  }
+  return value;
+}
+
 thread_local uint32_t current_thread_id_ = UINT_MAX;
 
 uint32_t current_thread_id() {

src/xenia/base/threading_win.cc

@@ -16,16 +16,6 @@
 namespace xe {
 namespace threading {
 
-uint32_t logical_processor_count() {
-  static uint32_t value = 0;
-  if (!value) {
-    SYSTEM_INFO system_info;
-    GetSystemInfo(&system_info);
-    value = system_info.dwNumberOfProcessors;
-  }
-  return value;
-}
-
 void EnableAffinityConfiguration() {
   HANDLE process_handle = GetCurrentProcess();
   DWORD_PTR process_affinity_mask;