Bug#19517 No simple way to detect wether server was compiled with libdbug

 - Define DBUG_ON and DBUG_OFF in config.h


configure.in:
  Define DBUG_ON and DBUG_OFF in config.h instead of in compiler flags
dbug/dbug.c:
  Undef DBUG_OFF if defined when compiling dbug.c, this is done as we always compile dbug.c even when DBUG_OFF is selected.

configure.in

@@ -1651,17 +1651,20 @@ AC_ARG_WITH(debug,
 if test "$with_debug" = "yes"
 then
   # Medium debug.
-  CFLAGS="$DEBUG_CFLAGS $DEBUG_OPTIMIZE_CC -DDBUG_ON -DSAFE_MUTEX $CFLAGS"
-  CXXFLAGS="$DEBUG_CXXFLAGS $DEBUG_OPTIMIZE_CXX -DDBUG_ON -DSAFE_MUTEX $CXXFLAGS"
+  AC_DEFINE([DBUG_ON], [1], [Use libdbug])
+  CFLAGS="$DEBUG_CFLAGS $DEBUG_OPTIMIZE_CC -DSAFE_MUTEX $CFLAGS"
+  CXXFLAGS="$DEBUG_CXXFLAGS $DEBUG_OPTIMIZE_CXX -DSAFE_MUTEX $CXXFLAGS"
 elif test "$with_debug" = "full"
 then
   # Full debug. Very slow in some cases
-  CFLAGS="$DEBUG_CFLAGS -DDBUG_ON -DSAFE_MUTEX -DSAFEMALLOC $CFLAGS"
-  CXXFLAGS="$DEBUG_CXXFLAGS -DDBUG_ON -DSAFE_MUTEX -DSAFEMALLOC $CXXFLAGS"
+  AC_DEFINE([DBUG_ON], [1], [Use libdbug])
+  CFLAGS="$DEBUG_CFLAGS -DSAFE_MUTEX -DSAFEMALLOC $CFLAGS"
+  CXXFLAGS="$DEBUG_CXXFLAGS -DSAFE_MUTEX -DSAFEMALLOC $CXXFLAGS"
 else
   # Optimized version. No debug
-  CFLAGS="$OPTIMIZE_CFLAGS -DDBUG_OFF $CFLAGS"
-  CXXFLAGS="$OPTIMIZE_CXXFLAGS -DDBUG_OFF $CXXFLAGS"
+  AC_DEFINE([DBUG_OFF], [1], [Don't use libdbug])
+  CFLAGS="$OPTIMIZE_CFLAGS $CFLAGS"
+  CXXFLAGS="$OPTIMIZE_CXXFLAGS $CXXFLAGS"
 fi
 
 # Force static compilation to avoid linking problems/get more speed

dbug/dbug.c

@@ -66,10 +66,13 @@
  *	Check of malloc on entry/exit (option "S")
  */
 
+#include <my_global.h>
+
+/* This file won't compile unless DBUG_OFF is undefined locally */
 #ifdef DBUG_OFF
 #undef DBUG_OFF
 #endif
-#include <my_global.h>
+
 #include <m_string.h>
 #include <errno.h>
 #if defined(MSDOS) || defined(__WIN__)