Reland "Enable PAC and BTI for runtime generated code."

This is a reland of commit c482a66b

Original change's description:
> Enable PAC and BTI for runtime generated code.
>
> This patch enables PAC and BTI for runtime generated code when PAC
> is enabled. Additional BTI landing pads will resolve to NOOP when
> running on non BTI device and will not cause functional problems.
>
> Change-Id: I3993481df2c3c47e3e81bfb76a8c355f642cd572
> Bug: chromium:919548, v8:10026
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3548457
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Andre Kempe <andre.kempe@arm.com>
> Cr-Commit-Position: refs/heads/main@{#79630}

Bug: chromium:919548, chromium:1310642, v8:10026
Change-Id: I5f76705a222b5f4fbc07cf472c02e9b58b5171fb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3579164Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Andre Kempe <andre.kempe@arm.com>
Cr-Commit-Position: refs/heads/main@{#79895}

BUILD.gn

@@ -474,7 +474,8 @@ if (v8_multi_arch_build &&
 # Check if it is a Chromium build and activate PAC/BTI if needed.
 # TODO(cavalcantii): have a single point of integration with PAC/BTI flags.
 if (build_with_chromium && v8_current_cpu == "arm64" &&
-    arm_control_flow_integrity == "standard") {
+    (arm_control_flow_integrity == "standard" ||
+     arm_control_flow_integrity == "pac")) {
   v8_control_flow_integrity = true
 }
 
@@ -1044,8 +1045,8 @@ config("toolchain") {
     defines += [ "V8_TARGET_ARCH_ARM64" ]
     if (current_cpu == "arm64") {
       # This will enable PAC+BTI in code generation and static code.
-      if (v8_control_flow_integrity) {
-        # TODO(v8:10026): Enable this in src/build.
+      if (v8_control_flow_integrity &&
+          (!build_with_chromium || arm_control_flow_integrity == "standard")) {
         cflags += [ "-mbranch-protection=standard" ]
         asmflags = [ "-mmark-bti-property" ]
       } else if (build_with_chromium && arm_control_flow_integrity == "pac") {