Merge pull request libgit2#6350 from libgit2/ethomson/zlib

zlib: update bundled zlib to v1.2.12

Author: ethomson

deps/zlib/adler32.c

@@ -177,3 +177,10 @@ uLong ZEXPORT adler32_combine(adler1, adler2, len2)
     return adler32_combine_(adler1, adler2, len2);
 }
 
+uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
+    uLong adler1;
+    uLong adler2;
+    z_off64_t len2;
+{
+    return adler32_combine_(adler1, adler2, len2);
+}