Factor common Vulkan build_overrides in vulkan_common.gni

This matches what's done in Chromium and was found while trying
to add a build override for VulkanMemoryAllocator.

Bug: tint:700
Bug: chromium:1195554
Change-Id: I50e71fb985169a89c03623b0959f57d5e43bb91a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2807714
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>

build_overrides/vulkan_common.gni

@@ -0,0 +1,12 @@
+# Copyright 2021 The ANGLE Project Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//gni/angle.gni")
+
+vulkan_headers_dir = angle_vulkan_headers_dir
+
+vulkan_data_subdir = angle_data_dir
+vulkan_gen_subdir = "angle/vulkan"
+
+vulkan_use_x11 = angle_use_x11

build_overrides/vulkan_headers.gni

@@ -2,6 +2,4 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//gni/angle.gni")
-
-vulkan_use_x11 = angle_use_x11
+import("//build_overrides/vulkan_common.gni")

build_overrides/vulkan_loader.gni

@@ -2,9 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//gni/angle.gni")
+import("//build_overrides/vulkan_common.gni")
 
-vulkan_headers_dir = angle_vulkan_headers_dir
-
-vulkan_gen_subdir = "angle/vulkan"
 vulkan_loader_shared = angle_shared_libvulkan

build_overrides/vulkan_memory_allocator.gni

@@ -0,0 +1,5 @@
+# Copyright 2021 The ANGLE Project Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//build_overrides/vulkan_common.gni")

build_overrides/vulkan_tools.gni

@@ -2,9 +2,4 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//gni/angle.gni")
-
-vulkan_headers_dir = angle_vulkan_headers_dir
-
-vulkan_data_subdir = angle_data_dir
-vulkan_gen_subdir = "angle/vulkan"
+import("//build_overrides/vulkan_common.gni")

build_overrides/vulkan_validation_layers.gni

@@ -2,11 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//gni/angle.gni")
+import("//build_overrides/vulkan_common.gni")
 
-vulkan_headers_dir = angle_vulkan_headers_dir
 vvl_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
 vvl_glslang_dir = "//third_party/vulkan-deps/glslang/src"
-
-vulkan_data_subdir = angle_data_dir
-vulkan_gen_subdir = "angle/vulkan"