Reland Update implementation of atomics with latest Chromium version but use compiler builtin atomi…

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 81980ed5d512450667f97a80e9211c051cb31903..9bc00378dd6c589433e1ad1d5fba594111b3dbd5 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2193,16 +2193,8 @@ v8_component("v8_libbase") {
     "src/base/adapters.h",
     "src/base/atomic-utils.h",
     "src/base/atomicops.h",
-    "src/base/atomicops_internals_arm64_gcc.h",
-    "src/base/atomicops_internals_arm_gcc.h",
     "src/base/atomicops_internals_atomicword_compat.h",
-    "src/base/atomicops_internals_mac.h",
-    "src/base/atomicops_internals_mips64_gcc.h",
-    "src/base/atomicops_internals_mips_gcc.h",
-    "src/base/atomicops_internals_s390_gcc.h",
-    "src/base/atomicops_internals_tsan.h",
-    "src/base/atomicops_internals_x86_gcc.cc",
-    "src/base/atomicops_internals_x86_gcc.h",
+    "src/base/atomicops_internals_portable.h",
     "src/base/atomicops_internals_x86_msvc.h",
     "src/base/base-export.h",
     "src/base/bits.cc",