Fix compile on chromeos-amd64-generic-cfi-thin-lto-rel

Follow-up to https://chromium-review.googlesource.com/c/chromium/src/+/3304484

Bug: 752720
Change-Id: I429f9a73d840cb089f39a3c88bd8e541aee3a7f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3305674
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/main@{#945798}

base/strings/string_util.cc

@@ -36,7 +36,8 @@ namespace base {
 bool IsWprintfFormatPortable(const wchar_t* format) {
   // This snippet of code checks that we can build C++17 code.
   // TODO(thakis): Enable this on all platforms, and then remove it again.
-#if !defined(OS_IOS) && !defined(OS_MAC) && !BUILDFLAG(CFI_ICALL_CHECK)
+#if !defined(OS_IOS) && !defined(OS_MAC) && !BUILDFLAG(CFI_ICALL_CHECK) && \
+    !BUILDFLAG(CFI_CAST_CHECK)
   if constexpr (constexpr int i = 0; i > 0) {
   }
 #endif