[win32] Make sure OS::Abort doesn't return

Fixes clang on windows warning:
..\..\v8\src\base\platform\platform-win32.cc(836,1) :
  error: function declared 'noreturn' should not return
   [-Werror,-Winvalid-noreturn]

CQ_INCLUDE_TRYBOTS=tryserver.chromium.win:win_clang_rel,win_clang_x64_rel

Review URL: https://codereview.chromium.org/1390193003

Cr-Commit-Position: refs/heads/master@{#31194}

src/base/platform/platform-win32.cc

@@ -833,6 +833,9 @@ void OS::Abort() {
   }
   // Make the MSVCRT do a silent abort.
   raise(SIGABRT);
+
+  // Make sure function doesn't return.
+  abort();
 }