Adapt upstream patches fixing potential deadlock in tcmalloc after fork.

base/allocator/BUILD.gn

Index: base/allocator/BUILD.gn
diff --git a/base/allocator/BUILD.gn b/base/allocator/BUILD.gn
index 0049800cb8620724cc14d2985aace93d85c195a7..0b2204645bd552198ba79a72d3ab478b8df35022 100644
--- a/base/allocator/BUILD.gn
+++ b/base/allocator/BUILD.gn
@@ -291,6 +291,10 @@ if (use_allocator == "tcmalloc") {
       configs += [ "//build/config/compiler:optimize_max" ]
     }
 
+    if (is_linux) {
+      defines += [ "HAVE_FORK" ]
+    }
+
     deps += [ "//base/third_party/dynamic_annotations" ]
   }
 }  # use_allocator == "tcmalloc"