Revert "Enable -Wunreachable-code in (non-arm) Chrome OS builds."

This reverts commit 2ff5fdbc.

Reason for revert: Causing compile failures on linux-chromeos-chrome
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-chrome/4233

Original change's description:
> Enable -Wunreachable-code in (non-arm) Chrome OS builds.
> 
> Bug: 1063529,346399
> Change-Id: I313ebf4cc16885d1f9bdc5a2ed8db524467735f2
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2116590
> Commit-Queue: Ben Pastene <bpastene@chromium.org>
> Reviewed-by: Ben Pastene <bpastene@chromium.org>
> Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
> Auto-Submit: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#752618}

TBR=oshima@chromium.org,thakis@chromium.org,bpastene@chromium.org

Change-Id: I01a4f609e3936fa98da9127d7f9858a4a61e2ecd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1063529, 346399
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2115865Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752723}

ash/display/display_prefs_unittest.cc

@@ -50,6 +50,12 @@
 namespace ash {
 
 namespace {
+const char kPrimaryIdKey[] = "primary-id";
+const char kPositionKey[] = "position";
+const char kOffsetKey[] = "offset";
+const char kPlacementDisplayIdKey[] = "placement.display_id";
+const char kPlacementParentDisplayIdKey[] = "placement.parent_display_id";
+
 bool IsRotationLocked() {
   return ash::Shell::Get()->screen_orientation_controller()->rotation_locked();
 }
@@ -508,13 +514,8 @@ TEST_F(DisplayPrefsTest, BasicStores) {
   EXPECT_EQ(id2, stored_placement.parent_display_id);
   EXPECT_EQ(id2, stored_layout.primary_id);
 
-  // TODO(oshima): Make the below pass and re-enable, https://crbug.com/1063529
-#if 0
-  const char kPrimaryIdKey[] = "primary-id";
-  const char kPositionKey[] = "position";
-  const char kOffsetKey[] = "offset";
-  const char kPlacementDisplayIdKey[] = "placement.display_id";
-  const char kPlacementParentDisplayIdKey[] = "placement.parent_display_id";
+  if (true)
+    return;
 
   std::string primary_id_str;
   EXPECT_TRUE(layout_value->GetString(kPrimaryIdKey, &primary_id_str));
@@ -608,7 +609,6 @@ TEST_F(DisplayPrefsTest, BasicStores) {
   EXPECT_TRUE(property->GetInteger("height", &height));
   EXPECT_EQ(500, width);
   EXPECT_EQ(400, height);
-#endif
 }
 
 TEST_F(DisplayPrefsTest, PreventStore) {

build/config/compiler/BUILD.gn

@@ -1591,10 +1591,8 @@ config("chromium_code") {
 
     # TODO(thakis): Enable this more often, https://crbug.com/346399
     # use_libfuzzer: https://crbug.com/1063180
-    # cros/arm has warnings in nacl code.
     if (!is_nacl && !use_libfuzzer &&
-        ((target_os == "chromeos" && target_cpu != "arm") ||
-         target_os == "fuchsia" || target_os == "linux")) {
+        (target_os == "fuchsia" || target_os == "linux")) {
       cflags += [ "-Wunreachable-code" ]
     }