Bug#36664672 Build break on Fedora 40 with debug and system libs

Use MY_Z_NULL in our own source code, to avoid macro redefinition:

In file included from <...>/mysql/storage/archive/ha_archive.h:32,
                 from <...>/mysql/storage/archive/ha_archive.cc:26:
<...>/mysql/storage/archive/azlib.h:198:9: error: "Z_NULL" redefined [-Werror]
  198 | #define Z_NULL 0 /* for initializing zalloc, zfree, opaque */
      |         ^~~~~~
In file included from <...>/mysql/storage/archive/ha_archive.h:25:
/usr/include/zlib.h:223:9: note: this is the location of the previous definition
  223 | #define Z_NULL  NULL  /* for compatibility with zlib, was for initializing zalloc, zfree, opaque */
      |         ^~~~~~

Change-Id: Ie333897dea2a8f29a07b3e8e90441396c19ed8f2

Author: Tor Didriksen

storage/archive/azio.cc

@@ -95,7 +95,7 @@ int az_open(azio_stream *s, const char *path, int Flags, File fd) {
     s->stream.next_out = s->outbuf;
     if (err != Z_OK) {
       destroy(s);
-      return Z_NULL;
+      return MY_Z_NULL;
     }
   } else {
     s->stream.next_in = s->inbuf;
@@ -109,7 +109,7 @@ int az_open(azio_stream *s, const char *path, int Flags, File fd) {
      */
     if (err != Z_OK) {
       destroy(s);
-      return Z_NULL;
+      return MY_Z_NULL;
     }
   }
   s->stream.avail_out = AZ_BUFSIZE_WRITE;
@@ -127,7 +127,7 @@ int az_open(azio_stream *s, const char *path, int Flags, File fd) {
 
   if (s->file < 0) {
     destroy(s);
-    return Z_NULL;
+    return MY_Z_NULL;
   }
 
   if (Flags & O_CREAT || Flags & O_TRUNC) {

storage/archive/azlib.h

@@ -195,7 +195,7 @@ extern "C" {
 #define Z_DEFLATED 8
 /* The deflate compression method (the only one supported in this version) */
 
-#define Z_NULL 0 /* for initializing zalloc, zfree, opaque */
+#define MY_Z_NULL 0 /* for initializing zalloc, zfree, opaque */
 #define AZ_BUFSIZE_READ 32768
 #define AZ_BUFSIZE_WRITE 16384