[libxml2] Avoid ignored attribute warnings under GCC

[Nick Wellnhofer <nwellnhof src gnome org>]

commit b88ae6d2e1c9f22931f59ff1ec490befe201fb26
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Oct 14 15:38:28 2019 +0200

    Avoid ignored attribute warnings under GCC
    
    GCC doesn't support the unsigned-integer-overflow sanitizer.

 dict.c | 4 ++++
 hash.c | 4 ++++
 2 files changed, 8 insertions(+)
---
diff --git a/dict.c b/dict.c
index fb0773b6..336e046a 100644
--- a/dict.c
+++ b/dict.c
@@ -372,7 +372,9 @@ found_pool:
  * http://burtleburtle.net/bob/hash/doobs.html
  */
 
+#ifdef __clang__
 ATTRIBUTE_NO_SANITIZE("unsigned-integer-overflow")
+#endif
 static uint32_t
 xmlDictComputeBigKey(const xmlChar* data, int namelen, int seed) {
     uint32_t hash;
@@ -405,7 +407,9 @@ xmlDictComputeBigKey(const xmlChar* data, int namelen, int seed) {
  *
  * Neither of the two strings must be NULL.
  */
+#ifdef __clang__
 ATTRIBUTE_NO_SANITIZE("unsigned-integer-overflow")
+#endif
 static unsigned long
 xmlDictComputeBigQKey(const xmlChar *prefix, int plen,
                       const xmlChar *name, int len, int seed)
diff --git a/hash.c b/hash.c
index f037af69..a83d979b 100644
--- a/hash.c
+++ b/hash.c
@@ -79,7 +79,9 @@ struct _xmlHashTable {
  * xmlHashComputeKey:
  * Calculate the hash key
  */
+#ifdef __clang__
 ATTRIBUTE_NO_SANITIZE("unsigned-integer-overflow")
+#endif
 static unsigned long
 xmlHashComputeKey(xmlHashTablePtr table, const xmlChar *name,
                  const xmlChar *name2, const xmlChar *name3) {
@@ -110,7 +112,9 @@ xmlHashComputeKey(xmlHashTablePtr table, const xmlChar *name,
     return (value % table->size);
 }
 
+#ifdef __clang__
 ATTRIBUTE_NO_SANITIZE("unsigned-integer-overflow")
+#endif
 static unsigned long
 xmlHashComputeQKey(xmlHashTablePtr table,
                   const xmlChar *prefix, const xmlChar *name,