Ignore Spectre mitigation warning.

VS2017 has added a new warning that indicates where Spectre mitigation
code would be inserted if /Qspectre were specified.

Change-Id: If80cd6a7d0c5a45313f4c3644b304cadecf465b0
Reviewed-on: https://boringssl-review.googlesource.com/28684
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 97ea289..89de7a8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -151,6 +151,8 @@
       "C4820" # 'bytes' bytes padding added after construct 'member_name'
       "C5026" # move constructor was implicitly defined as deleted
       "C5027" # move assignment operator was implicitly defined as deleted
+      "C5045" # Compiler will insert Spectre mitigation for memory load if
+              # /Qspectre switch specified
       )
   set(MSVC_LEVEL4_WARNINGS_LIST
       # See https://connect.microsoft.com/VisualStudio/feedback/details/1217660/warning-c4265-when-using-functional-header