Un-nest configs in GN files.

third_party/libusb/BUILD.gn

Index: third_party/libusb/BUILD.gn
diff --git a/third_party/libusb/BUILD.gn b/third_party/libusb/BUILD.gn
index cce639ea327da46bc41dc93d6468770a284f4bd0..82aeabd3790b918739d20f690143322320ec31cc 100644
--- a/third_party/libusb/BUILD.gn
+++ b/third_party/libusb/BUILD.gn
@@ -10,6 +10,17 @@ config("libusb_config") {
   include_dirs = [ "src/libusb" ]
 }
 
+config("libusb_warnings") {
+  visibility = [ ":*" ]
+  if (is_clang) {
+    # guid_eq in windows_usb.c is unused.
+    cflags = [ "-Wno-unused-function" ]
+    if (is_linux && !use_udev) {
+      cflags += [ "-Wno-pointer-sign" ]
+    }
+  }
+}
+
 static_library("libusb") {
   sources = [
     "src/config.h",
@@ -46,15 +57,6 @@ static_library("libusb") {
   deps = []
   include_dirs = [ "src/libusb/os" ]
 
-  config("libusb_warnings") {
-    if (is_clang) {
-      # guid_eq in windows_usb.c is unused.
-      cflags = [ "-Wno-unused-function" ]
-      if (is_linux && !use_udev) {
-        cflags += [ "-Wno-pointer-sign" ]
-      }
-    }
-  }
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
   configs += [ ":libusb_warnings" ]