Try a slightly rougher fix for libretro builds

(our builds work, but not their CI)

Common/Thread/ThreadUtil.cpp

@@ -16,7 +16,7 @@
 #include "Common/Log.h"
 #include "Common/Thread/ThreadUtil.h"
 
-#if defined(__ANDROID__) || defined(__APPLE__) || PPSSPP_PLATFORM(LINUX) || (defined(__GLIBC__) && defined(_GNU_SOURCE))
+#if defined(__ANDROID__) || defined(__APPLE__) || (defined(__GLIBC__) && defined(_GNU_SOURCE))
 #include <pthread.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -130,7 +130,11 @@ void AssertCurrentThreadName(const char *threadName) {
 }
 
 int GetCurrentThreadIdForDebug() {
-#if PPSSPP_PLATFORM(WINDOWS)
+#if __LIBRETRO__
+	// Not sure why gettid() would not be available, but it isn't.
+	// The return value of this function is only used in unit tests anyway...
+	return 1;
+#elif PPSSPP_PLATFORM(WINDOWS)
 	return (int)GetCurrentThreadId();
 #elif PPSSPP_PLATFORM(MAC) || PPSSPP_PLATFORM(IOS) || defined(__OpenBSD__) || defined(__FreeBSD__)
 	uint64_t tid = 0;