pw_build_info: Add missing header file for cmake

It should have been added in the following commit:
595fd95

Change-Id: I01db0da208d4cb0fd66601f7343d5413a912bf1f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/202210
Presubmit-Verified: CQ Bot Account <pigweed-scoped@luci-project-accounts.iam.gserviceaccount.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed-service-accounts.iam.gserviceaccount.com>
Pigweed-Auto-Submit: Armando Montanez <amontanez@google.com>
Reviewed-by: Kayce Basques <kayce@google.com>
Reviewed-by: Armando Montanez <amontanez@google.com>

pw_build_info/CMakeLists.txt

@@ -26,6 +26,7 @@ else()
   pw_add_library(pw_build_info.build_id STATIC
     HEADERS
       public/pw_build_info/build_id.h
+      public/pw_build_info/util.h
     PUBLIC_INCLUDES
       public
     PUBLIC_DEPS