Index: llvm/utils/gn/build/libs/zlib/BUILD.gn
===================================================================
--- llvm/utils/gn/build/libs/zlib/BUILD.gn
+++ llvm/utils/gn/build/libs/zlib/BUILD.gn
@@ -2,7 +2,13 @@
 
 config("zlib_config") {
   visibility = [ ":zlib" ]
-  libs = [ "z" ]
+  if (host_os == "win") {
+    assert(zlib_path != "", "Please provide the path to zlib")
+    include_dirs = [ zlib_path ]
+    libs = [ "$zlib_path/zlib.lib" ]
+  } else {
+    libs = [ "z" ]
+  }
 }
 
 group("zlib") {
Index: llvm/utils/gn/build/libs/zlib/enable.gni
===================================================================
--- llvm/utils/gn/build/libs/zlib/enable.gni
+++ llvm/utils/gn/build/libs/zlib/enable.gni
@@ -1,4 +1,11 @@
 declare_args() {
   # Whether to include code that links against zlib.
   llvm_enable_zlib = host_os != "win"
+
+  # Enabling zlib on Windows requires to provide the path to the .lib and
+  # its header files.
+  if (host_os == "win") {
+    # The path to zlib.lib and its corresponding header files.
+    zlib_path = ""
+  }
 }