Suppress psabi warnings in GN build.

These are disabled currently in the Android ARM GYP build. This patch disables it for all ARM builds since the warning appears when cross-compiling to ARM on Linux without Android (this isn't something people normally compile, so probably nobody noticed).

R=thakis@chromium.org

Review URL: https://codereview.chromium.org/299663014

git-svn-id: http://src.chromium.org/svn/trunk/src/build@271951 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

config/compiler/BUILD.gn

@@ -603,6 +603,12 @@ config("default_warnings") {
       ]
     }
 
+    # Suppress warnings about ABI changes on ARM (Clang doesn't give this
+    # warning).
+    if (cpu_arch == "arm" && !is_clang) {
+      cflags += [ "-Wno-psabi" ]
+    }
+
     if (is_android) {
       # Disable any additional warnings enabled by the Android build system but
       # which chromium does not build cleanly with (when treating warning as