libxl: expose #define to 4.5 and above

In e3abab74 (libxl: un-constify return value of libxl_basename), the
macro was exposed to releases < 4.5. However only new code is able to
make use of that macro so it should be exposed to releases >= 4.5.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl.h

@@ -478,13 +478,13 @@ typedef struct libxl__ctx libxl_ctx;
 #endif
 
 /*
- * LIBXL_HAVE_CONST_LIBXL_BASENAME_RETURN_VALUE
+ * LIBXL_HAVE_NONCONST_LIBXL_BASENAME_RETURN_VALUE
  *
  * The return value of libxl_basename is malloc'ed but the erroneously
  * marked as "const" in releases before 4.5.
  */
-#if defined(LIBXL_API_VERSION) && LIBXL_API_VERSION < 0x040500
-#define LIBXL_HAVE_CONST_LIBXL_BASENAME_RETURN_VALUE 1
+#if !defined(LIBXL_API_VERSION) || LIBXL_API_VERSION >= 0x040500
+#define LIBXL_HAVE_NONCONST_LIBXL_BASENAME_RETURN_VALUE 1
 #endif
 
 /*

tools/libxl/libxl_utils.c

@@ -19,7 +19,7 @@
 
 #include "libxl_internal.h"
 
-#ifdef LIBXL_HAVE_CONST_LIBXL_BASENAME_RETURN_VALUE
+#ifndef LIBXL_HAVE_NONCONST_LIBXL_BASENAME_RETURN_VALUE
 const
 #endif
 char *libxl_basename(const char *name)

tools/libxl/libxl_utils.h

@@ -18,7 +18,7 @@
 
 #include "libxl.h"
 
-#ifdef LIBXL_HAVE_CONST_LIBXL_BASENAME_RETURN_VALUE
+#ifndef LIBXL_HAVE_NONCONST_LIBXL_BASENAME_RETURN_VALUE
 const
 #endif
 char *libxl_basename(const char *name); /* returns string from strdup */