[arm64] Mark embedded builtins as supporting BTI

Use the recently added -mmark-bti-property Clang flag to add
GNU_PROPERTY_AARCH64_FEATURE_1_BTI to the ELF GNU program properties.

Bug: v8:10026
Change-Id: Id35a60c9f5a8b3019313d56a142ab8f481e095a5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2543934Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#71240}

BUILD.gn

@@ -721,6 +721,7 @@ config("toolchain") {
       # TODO(v8:10026): Enable this in src/build.
       if (current_cpu == "arm64") {
         cflags += [ "-mbranch-protection=standard" ]
+        asmflags = [ "-mmark-bti-property" ]
       }
     }
   }

src/snapshot/embedded/platform-embedded-file-writer-generic.cc

@@ -124,9 +124,7 @@ void PlatformEmbeddedFileWriterGeneric::DeclareFunctionBegin(const char* name,
 
 void PlatformEmbeddedFileWriterGeneric::DeclareFunctionEnd(const char* name) {}
 
-void PlatformEmbeddedFileWriterGeneric::FilePrologue() {
-  // TODO(v8:10026): Add ELF note required for BTI.
-}
+void PlatformEmbeddedFileWriterGeneric::FilePrologue() {}
 
 void PlatformEmbeddedFileWriterGeneric::DeclareExternalFilename(
     int fileid, const char* filename) {