Slightly DRY thread-setting code, fix warning

There were warnings from the rc variable being unused; this DRYes it to
use the same code as linux (including the failure check on rc).

llarp/util/thread/threading.cpp

@@ -23,7 +23,7 @@ namespace llarp
     void
     SetThreadName(const std::string& name)
     {
-#ifdef POSIX
+#if defined(POSIX) || __MINGW32__
 #if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__)
       /* on bsd this function has void return type */
       pthread_set_name_np(pthread_self(), name.c_str());
@@ -33,7 +33,7 @@ namespace llarp
 // API present upstream since v2.11.3 and imported downstream
 // in CR 8158 <https://www.illumos.org/issues/8158>
 // We only use the native function on Microsoft C++ builds
-#elif defined(__linux__) || defined(__sun)
+#elif defined(__linux__) || defined(__sun) || __MINGW32__
       const int rc = pthread_setname_np(pthread_self(), name.c_str());
 #else
 #error "unsupported platform"
@@ -46,8 +46,6 @@ namespace llarp
 #endif
 #elif _MSC_VER
       ::SetThreadName(::GetCurrentThreadId(), name.c_str());
-#elif __MINGW32__
-      const int rc = pthread_setname_np(pthread_self(), name.c_str());
 #else
       LogInfo("Thread name setting not supported on this platform");
       (void)name;