build: add configure flag to build V8 with DCHECKs

Add a configure flag that enables building V8 with `-DDEBUG`, in
particular with debug checks enabled and with runtime debugging
features, e.g. inspecting JS objects from debuggers, enabled.

PR-URL: #32787
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>

Author: addaleax

configure.py

@@ -635,6 +635,12 @@
     default=False,
     help='compile V8 with minimal optimizations and with runtime checks')
 
+parser.add_option('--v8-with-dchecks',
+    action='store_true',
+    dest='v8_with_dchecks',
+    default=False,
+    help='compile V8 with debug checks and runtime debugging features enabled')
+
 parser.add_option('--node-builtin-modules-path',
     action='store',
     dest='node_builtin_modules_path',
@@ -1235,6 +1241,7 @@ def configure_v8(o):
   o['variables']['v8_enable_gdbjit'] = 1 if options.gdb else 0
   o['variables']['v8_no_strict_aliasing'] = 1  # Work around compiler bugs.
   o['variables']['v8_optimized_debug'] = 0 if options.v8_non_optimized_debug else 1
+  o['variables']['dcheck_always_on'] = 1 if options.v8_with_dchecks else 0
   o['variables']['v8_random_seed'] = 0  # Use a random seed for hash tables.
   o['variables']['v8_promise_internal_field_count'] = 1 # Add internal field to promises for async hooks.
   o['variables']['v8_use_siphash'] = 0 if options.without_siphash else 1