Use inline asm to generate vctzlsbb

There was an issue in the way the vec_cnttz_lsbb builtin was being
implemented that got fixed on GCC 12, but now we have to use different
builtins depending on the compiler version. To avoid that, let's use
inline asm to generate the exact instruction we need.

contrib/power/longest_match_power9.c

@@ -11,6 +11,7 @@ local inline int vec_match OF((Bytef* scan, Bytef* match))
 local inline int vec_match(Bytef* scan, Bytef* match)
 {
     vector unsigned char vscan, vmatch, vc;
+    int len;
 
     vscan  = *((vector unsigned char *) scan);
     vmatch = *((vector unsigned char *) match);
@@ -25,7 +26,13 @@ local inline int vec_match(Bytef* scan, Bytef* match)
      * on vc (since we used cmpne), counting the number of consecutive
      * bytes where LSB == 0 is the same as counting the length of the match.
      */
-    return vec_cnttz_lsbb(vc);
+    #ifdef __LITTLE_ENDIAN__
+    asm volatile("vctzlsbb %0, %1\n\t" : "=r" (len) : "v" (vc));
+    #else
+    asm volatile("vclzlsbb %0, %1\n\t" : "=r" (len) : "v" (vc));
+    #endif
+
+   return len;
 }
 
 uInt ZLIB_INTERNAL _longest_match_power9(deflate_state *s, IPos cur_match)