thread/Thread: make IsInside() debug-only

This method is only used inside assert().

src/IOThread.cxx

@@ -108,8 +108,12 @@ io_thread_get() noexcept
 	return *io.loop;
 }
 
+#ifndef NDEBUG
+
 bool
 io_thread_inside() noexcept
 {
 	return io.thread.IsInside();
 }
+
+#endif

src/IOThread.hxx

@@ -20,6 +20,7 @@
 #ifndef MPD_IO_THREAD_HXX
 #define MPD_IO_THREAD_HXX
 
+#include "check.h"
 #include "Compiler.h"
 
 class EventLoop;
@@ -53,6 +54,8 @@ gcc_const
 EventLoop &
 io_thread_get() noexcept;
 
+#ifndef NDEBUG
+
 /**
  * Is the current thread the I/O thread?
  */
@@ -61,3 +64,5 @@ bool
 io_thread_inside() noexcept;
 
 #endif
+
+#endif

src/thread/Thread.hxx

@@ -64,6 +64,7 @@ public:
 #endif
 	}
 
+#ifndef NDEBUG
 	/**
 	 * Check if this thread is the current thread.
 	 */
@@ -81,6 +82,7 @@ public:
 		return pthread_self() == handle;
 #endif
 	}
+#endif
 
 	void Start();
 	void Join();