Force hidden symbol visibility for allocation operators

third_party/libc++/BUILD.gn

Index: third_party/libc++/BUILD.gn
diff --git a/third_party/libc++/BUILD.gn b/third_party/libc++/BUILD.gn
index ff51ab9260f771fcdafc6fa7f937bbe0dff607aa..8fc686b6d28b1a229a6bf3f6bd7cd4105216f0ca 100644
--- a/third_party/libc++/BUILD.gn
+++ b/third_party/libc++/BUILD.gn
@@ -98,6 +98,18 @@ target(link_target_type, "libc++") {
     "trunk/src/valarray.cpp",
     "trunk/src/variant.cpp",
   ]
+  if (libcpp_is_static) {
+    # Current gcc and clang do not allow declaring several allocation
+    # operators with hidden visibility [1] [2], however we don't want
+    # these symbols exported on static builds.  This is a workaround
+    # that takes advantage of an ELF visibility merging rule that
+    # picks the "most hidden" visibility of all versions of a symbol,
+    # even if the symbol is undefined.
+    #
+    # [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81107
+    # [2] https://bugs.llvm.org/show_bug.cgi?id=33473
+    sources += [ "alloc_visibility_overrides.S" ]
+  }
   configs -= [
     "//build/config/compiler:chromium_code",
     "//build/config/compiler:no_rtti",