Disable pointer conversion warning in XNVCtrl

src/third_party/libXNVCtrl/BUILD.gn

@@ -2,11 +2,27 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-static_library("libXNVCtrl") {
+# This warning disable must be appended to the command line after the general
+# warnings setup, so must be in a config.
+config("libXNVCtrl_config") {
+  # This will build under most configurations with this warning enabled, but
+  # some older system headers are missing a "const" on the third parameter of
+  # XextAddDisplay which will cause a failure.
+  cflags = [
+    "-Wno-incompatible-pointer-types-discards-qualifiers",
+  ]
+}
+
+source_set("libXNVCtrl") {
   sources = [
     "NVCtrl.c",
     "NVCtrl.h",
     "NVCtrlLib.h",
     "nv_control.h",
   ]
+
+  configs += [
+    ":libXNVCtrl_config",
+    "//build/config/linux:x11",
+  ]
 }