build: build v8 with -fvisibility=hidden on macOS

V8 should be built with -fvisibility=hidden, otherwise
the resulting binary would contain unnecessary symbols. In
particular, on macOS, this leads to 5000+ weak symbols
resolved at runtime, leading to a startup regression.

On macOS this also reduces the binary size about ~10MB.

It's only enabled on macOS in this patch as gcc can time out
or run out of memory on some machines in the CI with
-fvisibility=hidden.

PR-URL: #56275
Fixes: nodejs/performance#180
Reviewed-By: Juan José Arboleda <[email protected]>
Reviewed-By: Daniel Lemire <[email protected]>
Reviewed-By: Rafael Gonzaga <[email protected]>
Reviewed-By: Yagiz Nizipli <[email protected]>
Reviewed-By: Geoffrey Booth <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Chengzhong Wu <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>

tools/v8_gypfiles/v8.gyp

@@ -41,6 +41,19 @@
         'AdditionalOptions': ['/utf-8']
       }
     },
+    'conditions': [
+      ['OS=="mac"', {
+        # Hide symbols that are not explicitly exported with V8_EXPORT.
+        # TODO(joyeecheung): enable it on other platforms. Currently gcc times out
+        # or run out of memory with -fvisibility=hidden on some machines in the CI.
+        'xcode_settings': {
+          'GCC_SYMBOLS_PRIVATE_EXTERN': 'YES',  # -fvisibility=hidden
+        },
+        'defines': [
+          'BUILDING_V8_SHARED',  # Make V8_EXPORT visible.
+        ],
+      }],
+    ],
   },
   'targets': [
     {