Build third-party code with -Wall, build chromium_code with -Wextra on Linux

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 97eb6726ca36455f5b87284c80ecc8c85f8c875e..88dba49ae0ec4b68de8f2f8281a02e92b0074ab3 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -894,15 +894,14 @@ config("chromium_code") {
   if (is_win) {
     cflags = [ "/W4" ]  # Warning level 4.
   } else {
-    cflags = [
-      "-Wall",
+    cflags = [ "-Wall" ]
 
-      # GCC turns on -Wsign-compare for C++ under -Wall, but clang doesn't,
-      # so we specify it explicitly.
-      # TODO(fischman): remove this if http://llvm.org/PR10448 obsoletes it.
-      # http://code.google.com/p/chromium/issues/detail?id=90453
-      "-Wsign-compare",
-    ]
+    # TODO(thakis): Remove !is_nacl once
+    # https://codereview.webrtc.org/1552863002/ made its way into chromium.
+    if (is_clang && !is_nacl) {
+      # Enable -Wextra when we control the compiler.
+      cflags += [ "-Wextra" ]
+    }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.
@@ -944,6 +943,10 @@ config("no_chromium_code") {
       "_CRT_NONSTDC_NO_WARNINGS",
       "_CRT_NONSTDC_NO_DEPRECATE",
     ]
+  } else if (is_clang && !is_nacl) {
+    # TODO(thakis): Remove !is_nacl once
+    # https://codereview.webrtc.org/1552863002/ made its way into chromium.
+    cflags += [ "-Wall" ]
   }
 
   if (is_linux) {