Enables GN build on windows

runtime/bin/BUILD.gn

Index: runtime/bin/BUILD.gn
diff --git a/runtime/bin/BUILD.gn b/runtime/bin/BUILD.gn
index d8a638446ae376633fb61c2abc44184df527e7d9..df8d40573e828456e08eff7b8e29a4e600c17c00 100644
--- a/runtime/bin/BUILD.gn
+++ b/runtime/bin/BUILD.gn
@@ -203,9 +203,11 @@ gen_library_src_path("generate_web_audio_cc_file") {
 }
 
 config("libdart_builtin_config") {
-  libs = [
-    "dl",
-  ]
+  if (!is_win) {
+    libs = [
+      "dl",
+    ]
+  }
   if (is_android) {
     libs += [
       "android",
@@ -300,6 +302,16 @@ executable("gen_snapshot") {
       "CoreServices.framework"
     ]
   }
+
+  if (is_win) {
+    libs = [
+      "iphlpapi.lib",
+      "psapi.lib",
+      "ws2_32.lib",
+      "Rpcrt4.lib",
+      "winmm.lib",
+    ]
+  }
 }
 
 # A source set for the implementation of 'dart:io' library
@@ -545,9 +557,25 @@ template("dart_executable") {
       "//third_party",
     ]
 
-    ldflags = [
-      "-rdynamic",
-    ]
+    if (is_win) {
+      ldflags = [
+        "/EXPORT:Dart_True"
+      ]
+    } else {
+      ldflags = [
+        "-rdynamic",
+      ]
+    }
+
+    if (is_win) {
+      libs = [
+        "iphlpapi.lib",
+        "psapi.lib",
+        "ws2_32.lib",
+        "Rpcrt4.lib",
+        "winmm.lib",
+      ]
+    }
   }
 }
 
@@ -719,9 +747,21 @@ executable("run_vm_tests") {
     "run_vm_tests.cc",
   ] + builtin_impl_tests_list.sources + vm_tests
 
-  ldflags = [
-    "-rdynamic",
-  ]
+  if (!is_win) {
+    ldflags = [
+      "-rdynamic",
+    ]
+  }
+
+  if (is_win) {
+    libs = [
+      "iphlpapi.lib",
+      "psapi.lib",
+      "ws2_32.lib",
+      "Rpcrt4.lib",
+      "winmm.lib",
+    ]
+  }
 }
 
 if (!defined(is_fuchsia) || !is_fuchsia) {
@@ -740,6 +780,15 @@ if (!defined(is_fuchsia) || !is_fuchsia) {
       # The only effect of DART_SHARED_LIB is to export the Dart API.
       "DART_SHARED_LIB",
     ]
+    if (is_win) {
+      libs = [
+        "dart.lib"
+      ]
+      abs_root_out_dir = rebase_path(root_out_dir)
+      ldflags = [
+        "/LIBPATH:$abs_root_out_dir"
+      ]
+    }
   }
 
   shared_library("sample_extension") {
@@ -757,5 +806,14 @@ if (!defined(is_fuchsia) || !is_fuchsia) {
       # The only effect of DART_SHARED_LIB is to export the Dart API.
       "DART_SHARED_LIB",
     ]
+    if (is_win) {
+      libs = [
+        "dart.lib"
+      ]
+      abs_root_out_dir = rebase_path(root_out_dir)
+      ldflags = [
+        "/LIBPATH:$abs_root_out_dir"
+      ]
+    }
   }
 }