[gn] introduce v8_expose_symbols for symbol visibility

TBR=sergiyb@chromium.org

Bug: v8:8840
Change-Id: I04c2e6a1703764416cbb9987de262fe4d2b86b14
Reviewed-on: https://chromium-review.googlesource.com/c/1470105Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59572}

gni/v8.gni

@@ -53,6 +53,9 @@ declare_args() {
 
   # Enable monolithic static library for embedders.
   v8_monolithic = false
+
+  # Expose symbols for dynamic linking.
+  v8_expose_symbols = false
 }
 
 if (v8_use_external_startup_data == "") {
@@ -113,7 +116,8 @@ if (v8_code_coverage && !is_clang) {
   ]
 }
 
-if ((is_posix || is_fuchsia) && (v8_enable_backtrace || v8_monolithic)) {
+if ((is_posix || is_fuchsia) &&
+    (v8_enable_backtrace || v8_monolithic || v8_expose_symbols)) {
   v8_remove_configs += [ "//build/config/gcc:symbol_visibility_hidden" ]
   v8_add_configs += [ "//build/config/gcc:symbol_visibility_default" ]
 }