Update GN files w/ changes needed to make sanitizers work.

build/toolchain/gcc_toolchain.gni

Index: build/toolchain/gcc_toolchain.gni
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index 7db87a3b10151df5bf9d841ec8e5c6a97aff20de..0ae75a70d24f899c5baeb22d0da8c01c03cfdedb 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -482,7 +482,17 @@ template("gcc_toolchain") {
       is_syzyasan = false
       is_tsan = false
       is_ubsan = false
+      is_ubsan_no_recover = false
+      is_ubsan_security = false
       is_ubsan_vptr = false
+      msan_track_origins = 0
+      sanitizer_coverage_flags = ""
+      use_cfi_diag = false
+      use_custom_libcxx = false
+      use_drfuzz = false
+      use_libfuzzer = false
+      use_prebuilt_instrumented_libraries = false
+      use_sanitizer_coverage = false
     }
 
     forward_variables_from(invoker, [ "deps" ])