Fix repeated "-Wunknown-pragmas -Wno-error=unknown-pragmas".

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 8f5712039c167f581c359ebcc3ded33bf3fc076c..894a806168c14f91e2dd67f92e75c477b1f1a0c8 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1691,6 +1691,20 @@ config("no_symbols") {
   }
 }
 
+# On Linux and Android, the "grit" template wants to disable the warning about
+# unknown pragmas. However since gn does not deduplicate the flags from configs
+# but only the config themselves, if the template declares a "config" for that
+# purpose, the flag will end up being repeated for each dependent "grit" target.
+# Using a separate config solves this problem.
+config("disable_unknown_pragma") {
+  if (is_clang) {
+    cflags = [
+      "-Wunknown-pragmas",
+      "-Wno-error=unknown-pragmas",
+    ]
+  }
+}
+
 # Default symbols.
 config("default_symbols") {
   if (symbol_level == 0) {