Reland "[ptr-compr][x64] Temporarily enable pointer compression on x64"

This is a reland of 4f051fd5

Relanding because last revert was caused by unrelated flakes.

Original change's description:
> [ptr-compr][x64] Temporarily enable pointer compression on x64
>
> ... and make sure that the x64 ptr-compr bots proceed testing V8 without
> pointer compression in order to keep testing the full pointer mode.
>
> Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng,v8_linux64_tsan_rel
> Bug: v8:7703
> Change-Id: Ied4e7bacf99c9d63e0459613fec522273f595de8
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1523327
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#60339}

Bug: v8:7703
Change-Id: I9c588de77070d4fbf1bb1a21ae58c398a22eed9c
Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng, v8_linux64_tsan_rel, v8_mac64_gc_stress_dbg
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1530819
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60370}

BUILD.gn

@@ -98,7 +98,7 @@ declare_args() {
   v8_enable_verify_csa = false
 
   # Enable pointer compression (sets -dV8_COMPRESS_POINTERS).
-  v8_enable_pointer_compression = false
+  v8_enable_pointer_compression = ""
   v8_enable_31bit_smis_on_64bit_arch = false
 
   # Sets -dOBJECT_PRINT.
@@ -212,6 +212,11 @@ if (v8_check_microtasks_scopes_consistency == "") {
       v8_enable_debugging_features || dcheck_always_on
 }
 
+if (v8_enable_pointer_compression == "") {
+  # TODO(v8:v7703): temporarily enable pointer compression on x64
+  v8_enable_pointer_compression = v8_current_cpu == "x64"
+}
+
 assert(v8_current_cpu != "x86" || !v8_untrusted_code_mitigations,
        "Untrusted code mitigations are unsupported on ia32")
 

infra/mb/mb_config.pyl

@@ -447,7 +447,10 @@
       'release_bot', 'x64', 'minimal_symbols'],
     'release_x64_pointer_compression': [
       'release_bot', 'x64', 'dcheck_always_on', 'v8_enable_slow_dchecks',
-      'v8_enable_pointer_compression'],
+      # TODO(v8:v7703): Make pointer compression bots testing non pointer
+      # compression mode while pointer compression is temporarily enabled
+      # on x64
+      'v8_disable_pointer_compression'],
     'release_x64_trybot': [
       'release_trybot', 'x64'],
     'release_x64_test_features_trybot': [
@@ -800,6 +803,10 @@
       'gn_args': 'v8_enable_pointer_compression=true',
     },
 
+    'v8_disable_pointer_compression': {
+      'gn_args': 'v8_enable_pointer_compression=false',
+    },
+
     'v8_enable_test_features': {
       'gn_args': 'v8_enable_test_features=true',
     },