build,src: gate jspi flag on V8_ENABLE_WEBASSEMBLY

Since d937c8c ("wasm: enable JSPI") ProcessGlobalArgsInternal()
unconditionally appends --experimental-wasm-jspi to the V8 argument
list. V8 only defines the experimental_wasm_* flags when it is built
with V8_ENABLE_WEBASSEMBLY, and configure --v8-lite-mode sets
v8_enable_webassembly=0. V8::SetFlagsFromCommandLine() is called with
remove_flags=true, which silently leaves unrecognized flags in argv, so
node reports "bad option: --experimental-wasm-jspi" and exits with
kInvalidCommandLineArgument. The first binary to run that code is
node_mksnapshot, so every --v8-lite-mode build has failed since
v24.20.0:

  bad option: --experimental-wasm-jspi
  node_mksnapshot failed with exit code 9

Forward v8_enable_webassembly to all targets as V8_ENABLE_WEBASSEMBLY,
the same way common.gypi already forwards the other V8 build flags, and
only push the JSPI flag when WebAssembly is compiled in.

Refs: #59941
Assisted-by: claude:fable-5.1
Signed-off-by: Piotr Kubaj <pkubaj@FreeBSD.org>

Author: pkubaj

common.gypi

@@ -75,6 +75,9 @@
     # Disable v8 hugepage by default.
     'v8_enable_hugepage%': 0,
 
+    # Disabled by configure --v8-lite-mode.
+    'v8_enable_webassembly%': 1,
+
     # This is more of a V8 dev setting
     # https://github.com/nodejs/node/pull/22920/files#r222779926
     'v8_enable_fast_mksnapshot': 0,
@@ -509,6 +512,9 @@
       ['v8_enable_v8_checks == 1', {
         'defines': ['V8_ENABLE_CHECKS'],
       }],
+      ['v8_enable_webassembly == 1', {
+        'defines': ['V8_ENABLE_WEBASSEMBLY'],
+      }],
       ['v8_enable_pointer_compression == 1', {
         'defines': ['V8_COMPRESS_POINTERS'],
       }],

src/node.cc

@@ -786,8 +786,10 @@ static ExitCode ProcessGlobalArgsInternal(std::vector<std::string>* args,
     v8_args.emplace_back("--js-source-phase-imports");
   }
 
+#if V8_ENABLE_WEBASSEMBLY
   // WebAssembly JS Promise Integration
   v8_args.emplace_back("--experimental-wasm-jspi");
+#endif  // V8_ENABLE_WEBASSEMBLY
 
 #ifdef __POSIX__
   // Block SIGPROF signals when sleeping in epoll_wait/kevent/etc.  Avoids the