Add additional import for is_ubsan

This CL adds an import of //build/config/sanitizers/sanitizers.gni for
the is_ubsan variable.

Bug: 475855993
Change-Id: Ieba020434f4f982dcdc3a469b0b899d04e8e4b62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7882511
Commit-Queue: Rick Byers <rbyers@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1638841}
NOKEYCHECK=True
GitOrigin-RevId: 88ca82ad9563fea4525d1a497fbe25fe0c79e62b

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 0a9eb55..02237cc 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//build/config/gclient_args.gni")
+import("//build/config/sanitizers/sanitizers.gni")
 
 if (build_with_chromium) {
   import("//testing/libfuzzer/fuzzer_test.gni")