[docs] Update cross compilation .gclient setup and instructions.

Bug: None
Change-Id: Ibdcae0a7e8ccba6366c1d7aacb01fa06d8181b2e
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/319335
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Auto-Submit: Loko Kung <lokokung@google.com>
Commit-Queue: Loko Kung <lokokung@google.com>

docs/building.md

diff --git a/docs/building.md b/docs/building.md
index 31a1ada..9d2e185 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -97,6 +97,7 @@
 
 The following packages are needed to build Dawn. (Package names are the Ubuntu names).
 
+* `libfuse2`
 * `libxrandr-dev`
 * `libxinerama-dev`
 * `libxcursor-dev`
@@ -107,7 +108,7 @@
 * `npm`
 
 ```sh
-sudo apt-get install libxrandr-dev libxinerama-dev libxcursor-dev mesa-common-dev libx11-xcb-dev pkg-config nodejs npm
+sudo apt-get install libfuse2 libxrandr-dev libxinerama-dev libxcursor-dev mesa-common-dev libx11-xcb-dev pkg-config nodejs npm
 ```
 
 Note, `nodejs` and `npm` are only needed if building `dawn.node`.
@@ -162,8 +163,8 @@
 of compilation checks during local Dawn development. It only supports Clang.
 It may not always work, and the resulting binaries are not guaranteed to work.
 
-1.  Add your target OS to the `target_os` array in `.gclient`. Or, just use
-    `standalone-maximal.gclient`.
+1.  Add your target OS to the `target_os` array in `.gclient`. Or, use
+    `standalone-maximal.gclient` and follow the instructions in it.
 1.  `gclient sync`.
 1.  Create a new `out/*` directory for each target build with the relevant GN
     args. The following configurations have been tested:

scripts/standalone-maximal.gclient

diff --git a/scripts/standalone-maximal.gclient b/scripts/standalone-maximal.gclient
index 9a29619..0a4bc3c 100644
--- a/scripts/standalone-maximal.gclient
+++ b/scripts/standalone-maximal.gclient
@@ -1,11 +1,12 @@
 # Copy this file to <dawn clone dir>/.gclient to bootstrap gclient in a
-# standalone checkout of Dawn for building emdawnwebgpu using emsdk.
+# standalone checkout of Dawn for maximal target support including
+# building cross compilation, emscripten builds, and node builds. After
+# copying this file, users should uncomment the respective lines below
+# based on the host OS.
 #
 # Use this instead of `standalone.gclient` if you are a Dawn developer and
 # would like to compile as much as possible on your local machine.
 
-import platform
-
 solutions = [
     {
         "name": ".",
@@ -24,7 +25,7 @@
 
 # Enable all additional targets that are usable on this host OS.
 target_os = []
-if platform.system() == "Darwin":
-    target_os += ['win']
-elif platform.system() == "Linux":
-    target_os += ['win', 'mac']
+# If cross compiling on Mac, uncomment this:
+#target_os += ['win']
+# If cross compiling on Linux, uncomment this:
+#target_os += ['win', 'mac']
\ No newline at end of file