[platform] Mark OS::ExitProcess as [[noreturn]]

Just as OS::Abort, OS::ExitProcess never returns. This is a minor
cleanup which is not expected to reduce binary size considerably, since
we do not call this function often. It is just nice to annotate it
correctly.
On windows, the {TerminateProcess} call is known to not return if
called on the current process. Add an {UNREACHABLE} to enforce this.

R=mlippautz@chromium.org

Bug: v8:11074
Change-Id: I5c079fc459685c65f932404ce536ea28ad188073
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2536634Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71210}

src/base/platform/platform-win32.cc

@@ -502,11 +502,15 @@ int OS::GetCurrentThreadId() {
 }
 
 void OS::ExitProcess(int exit_code) {
-  // Use TerminateProcess avoid races between isolate threads and
+  // Use TerminateProcess to avoid races between isolate threads and
   // static destructors.
   fflush(stdout);
   fflush(stderr);
   TerminateProcess(GetCurrentProcess(), exit_code);
+  // Termination the current process does not return. {TerminateProcess} is not
+  // marked [[noreturn]] though, since it can also be used to terminate another
+  // process.
+  UNREACHABLE();
 }
 
 // ----------------------------------------------------------------------------

src/base/platform/platform.h

@@ -263,7 +263,7 @@ class V8_BASE_EXPORT OS {
 
   static void AdjustSchedulingParams();
 
-  static void ExitProcess(int exit_code);
+  [[noreturn]] static void ExitProcess(int exit_code);
 
  private:
   // These classes use the private memory management API below.