gn: Fix build on Windows

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 797f473425454875ed895b231e91bba3a923bc66..9b82ae42427317d5fbc667c18c30dd36b7e930e1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -41,7 +41,21 @@ config("libvpx_config") {
     "//third_party/libvpx/source/libvpx",
     "$root_gen_dir/third_party/libvpx", # Provides vpx_rtcd.h.
   ]
-  cflags = [ "-Wno-unused-function", "-Wno-sign-compare" ]
+  if (is_win) {
+    cflags = [
+      "/wd4057",

[Johann, 2014/09/25 21:00:25]

We (try) to track Windows errors pretty carefully and have removed all the
warnings we're aware of in both our local builds and Chromium. Has something
changed in GN that warnings which were not enabled in GYP are now turned on?

+      "/wd4201",
+      "/wd4204",
+      "/wd4221",
+      "/wd4245",
+      "/wd4324",
+      "/wd4389",
+      "/wd4701",
+      "/wd4706",
+    ]
+  } else {
+    cflags = [ "-Wno-unused-function", "-Wno-sign-compare" ]
+  }
 }
 
 # This config is applied to targets that depend on libvpx.
@@ -93,11 +107,17 @@ template("obj_int_extract") {
       args += [ "-f", "rvds" ]
     }
 
+    if (is_win) {
+      obj_extension = "obj"
+    } else {
+      obj_extension = "o"
+    }
+
     args += [
       "-b",
       rebase_path(get_label_info(":libvpx_asm_offsets", "target_out_dir")) +
           "/" + invoker.src_dir + "/libvpx_asm_offsets." +
-          invoker.obj_file_root + ".o"
+          invoker.obj_file_root + ".${obj_extension}"
     ]
     out_file = "$target_gen_dir/" + invoker.obj_file_root + ".asm"
     args += [ "-o", rebase_path(out_file) ]
@@ -143,7 +163,9 @@ if (cpu_arch == "x86" || cpu_arch == "x64") {
 
 static_library("libvpx_intrinsics_mmx") {
   configs += [ ":libvpx_config" ]
-  cflags = [ "-mmmx" ]
+  if (!is_win) {
+    cflags = [ "-mmmx" ]
+  }
   if (cpu_arch == "x86") {
     sources = libvpx_srcs_x86_mmx
   } else if (cpu_arch == "x64") {
@@ -153,7 +175,9 @@ static_library("libvpx_intrinsics_mmx") {
 
 static_library("libvpx_intrinsics_sse2") {
   configs += [ ":libvpx_config" ]
-  cflags = [ "-msse2" ]
+  if (!is_win) {
+    cflags = [ "-msse2" ]
+  }
   if (cpu_arch == "x86") {
     sources = libvpx_srcs_x86_sse2
   } else if (cpu_arch == "x64") {
@@ -163,7 +187,9 @@ static_library("libvpx_intrinsics_sse2") {
 
 static_library("libvpx_intrinsics_ssse3") {
   configs += [ ":libvpx_config" ]
-  cflags = [ "-mssse3" ]
+  if (!is_win) {
+    cflags = [ "-mssse3" ]
+  }
   if (cpu_arch == "x86") {
     sources = libvpx_srcs_x86_ssse3
   } else if (cpu_arch == "x64") {
@@ -173,7 +199,9 @@ static_library("libvpx_intrinsics_ssse3") {
 
 static_library("libvpx_intrinsics_sse4_1") {
   configs += [ ":libvpx_config" ]
-  cflags = [ "-msse4.1" ]
+  if (!is_win) {
+    cflags = [ "-msse4.1" ]
+  }
   if (cpu_arch == "x86") {
     sources = libvpx_srcs_x86_sse4_1
   } else if (cpu_arch == "x64") {