gn2bp: Add `-Wno-null-pointer-subtraction` to the default flags

Test: m cronet_aml_components_cronet_android_cronet
Change-Id: I129160617c30b977a39400a91d10ab8a5e61cb8f
diff --git a/tools/gn2bp/Android.bp.swp b/tools/gn2bp/Android.bp.swp
index 3255e5b..24e09cc 100644
--- a/tools/gn2bp/Android.bp.swp
+++ b/tools/gn2bp/Android.bp.swp
@@ -5103,6 +5103,7 @@
         "-Wno-macro-redefined",
         "-Wno-missing-field-initializers",
         "-Wno-non-virtual-dtor",
+        "-Wno-null-pointer-subtraction",
         "-Wno-sign-compare",
         "-Wno-sign-promo",
         "-Wno-unreachable-code-loop-increment",