Port r282246 to gn.

Temporarily disable -Werror on linux, since the gn build isn't yet
warning-free with clang. Since gn doesn't use -Werror for all targets yet
anyways (http://crbug.com/393046) that seems acceptable.

BUG=360311,393046
R=brettw@chromium.org

Review URL: https://codereview.chromium.org/387693002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@284372 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/BUILDCONFIG.gn

@@ -31,7 +31,7 @@ declare_args() {
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
-  is_clang = (os == "mac" || os == "ios")
+  is_clang = (os == "mac" || os == "ios" || os == "linux")
 
   # Forces a 64-bit build on Windows. Does nothing on other platforms. Normally
   # we build 32-bit on Windows regardless of the current host OS bit depth.

config/compiler/BUILD.gn

@@ -451,6 +451,8 @@ config("runtime_library") {
 # Toggles between higher and lower warnings for code that is (or isn't)
 # part of Chromium.
 
+# TODO: -Werror and /WX should always be on, independent of chromium_code
+# http://crbug.com/393046
 config("chromium_code") {
   if (is_win) {
     cflags = [
@@ -460,7 +462,6 @@ config("chromium_code") {
   } else {
     cflags = [
       "-Wall",
-      "-Werror",
 
       # GCC turns on -Wsign-compare for C++ under -Wall, but clang doesn't,
       # so we specify it explicitly.
@@ -468,6 +469,11 @@ config("chromium_code") {
       # http://code.google.com/p/chromium/issues/detail?id=90453
       "-Wsign-compare",
     ]
+    if (!is_linux) {
+      # TODO: Add this unconditionally once linux builds without warnings with
+      # clang in the gn build.
+      cflags += [ "-Werror" ]
+    }
 
     # In Chromium code, we define __STDC_foo_MACROS in order to get the
     # C99 macros on Mac and Linux.