Set using_sanitizer if use_cfi_diag is true.

build/config/sanitizers/sanitizers.gni

Index: build/config/sanitizers/sanitizers.gni
diff --git a/build/config/sanitizers/sanitizers.gni b/build/config/sanitizers/sanitizers.gni
index f59770a4148ea348f0bdeb9c22d946fa873df75a..cb8bbfb1c4b997f12fde552eb3abcdb9a44be88f 100644
--- a/build/config/sanitizers/sanitizers.gni
+++ b/build/config/sanitizers/sanitizers.gni
@@ -163,9 +163,12 @@ if ((use_afl || use_libfuzzer) && sanitizer_coverage_flags == "") {
   sanitizer_coverage_flags = "trace-pc-guard,indirect-calls"
 }
 
+# Whether we are linking against a sanitizer runtime library. Among other
+# things, this changes the default symbol level and other settings in order to
+# prepare to create stack traces "live" using the sanitizer runtime.
 using_sanitizer =
     is_asan || is_lsan || is_tsan || is_msan || is_ubsan || is_ubsan_null ||
-    is_ubsan_vptr || is_ubsan_security || use_sanitizer_coverage
+    is_ubsan_vptr || is_ubsan_security || use_sanitizer_coverage || use_cfi_diag
 
 assert(!using_sanitizer || is_clang,
        "Sanitizers (is_*san) require setting is_clang = true in 'gn args'")