[libxml2] NaN and Inf fixes for pre-C99 compilers

[Nick Wellnhofer <nwellnhof src gnome org>]

commit 7abec671473b837f99181442d59edd0cc2ee01d1
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Thu Mar 15 19:33:52 2018 +0100

    NaN and Inf fixes for pre-C99 compilers
    
    On some pre-C99 compilers, the NAN and INFINITY macros don't expand to
    constant expressions.
    
    Some MSVC versions complain about floating point division by zero in
    constants.
    
    Thanks to Fabrice Manfroi for the report.

 xpath.c |   19 ++++++++++---------
 1 files changed, 10 insertions(+), 9 deletions(-)
---
diff --git a/xpath.c b/xpath.c
index f440696..89fab58 100644
--- a/xpath.c
+++ b/xpath.c
@@ -477,27 +477,28 @@ int wrap_cmp( xmlNodePtr x, xmlNodePtr y );
  *                                                                     *
  ************************************************************************/
 
-#ifndef NAN
-#define NAN (0.0 / 0.0)
+#ifndef INFINITY
+#define INFINITY (DBL_MAX * DBL_MAX)
 #endif
 
-#ifndef INFINITY
-#define INFINITY HUGE_VAL
+#ifndef NAN
+#define NAN (INFINITY / INFINITY)
 #endif
 
-double xmlXPathNAN = NAN;
-double xmlXPathPINF = INFINITY;
-double xmlXPathNINF = -INFINITY;
+double xmlXPathNAN;
+double xmlXPathPINF;
+double xmlXPathNINF;
 
 /**
  * xmlXPathInit:
  *
  * Initialize the XPath environment
- *
- * Does nothing but must be kept as public function.
  */
 void
 xmlXPathInit(void) {
+    xmlXPathNAN = NAN;
+    xmlXPathPINF = INFINITY;
+    xmlXPathNINF = -INFINITY;
 }
 
 /**