Fix MSVC compiler error in platform-embedded-file-writer-win.cc.

This file did not include all the headers it needed, so when
https://crrev.com/c/3749178 removed a bunch of headers, the MSVC build
broke. Add in the missing header to address the MSVC compiler falure.

Change-Id: I646787cfde802d8cabe7d61bac2f2066beaec436
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3764190Reviewed-by: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81790}

src/snapshot/embedded/platform-embedded-file-writer-win.cc

@@ -15,6 +15,10 @@
 #include "src/snapshot/embedded/embedded-file-writer.h"
 #endif  // V8_OS_WIN64
 
+#if defined(V8_COMPILER_IS_MSVC)
+#include "src/flags/flags.h"
+#endif
+
 namespace v8 {
 namespace internal {