Add GN rules for building instrumented libraries.

build/config/BUILD.gn

Index: build/config/BUILD.gn
diff --git a/build/config/BUILD.gn b/build/config/BUILD.gn
index 4934afae59a08910cd81e04d5c3b44be295f82bb..9e352eb4d5c3c139320c94e42ef8d9f7574855e9 100644
--- a/build/config/BUILD.gn
+++ b/build/config/BUILD.gn
@@ -403,6 +403,9 @@ config("executable_config") {
   if (prebuilt_instrumented_libraries_available) {
     configs += [ "//third_party/instrumented_libraries:prebuilt_ldflags" ]
   }
+  if (use_locally_built_instrumented_libraries) {
+    configs += [ "//third_party/instrumented_libraries:locally_built_ldflags" ]
+  }
 }
 
 # Shared library configs -------------------------------------------------------
@@ -424,6 +427,9 @@ config("shared_library_config") {
   if (prebuilt_instrumented_libraries_available) {
     configs += [ "//third_party/instrumented_libraries:prebuilt_ldflags" ]
   }
+  if (use_locally_built_instrumented_libraries) {
+    configs += [ "//third_party/instrumented_libraries:locally_built_ldflags" ]
+  }
 }
 
 # Add this config to your target to enable precompiled headers.