Silence C4709 in MSVC because it is buggy.

The diagnostic will trigger on code that does not have any comma operator, but instead default-constructs an object with an explicitly defaulted constructor as the array index argument.

llvm-svn: 347345
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 56145e9..49db308 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -513,6 +513,10 @@
           # Update 1. Re-evaluate the usefulness of this diagnostic with Update 2.
       -wd4592 # Suppress ''var': symbol will be dynamically initialized (implementation limitation)
       -wd4319 # Suppress ''operator' : zero extending 'type' to 'type' of greater size'
+          # C4709 is disabled because of a bug with Visual Studio 2017 as of
+          # v15.8.8. Re-evaluate the usefulness of this diagnostic when the bug
+          # is fixed.
+      -wd4709 # Suppress comma operator within array index expression
 
       # Ideally, we'd like this warning to be enabled, but MSVC 2013 doesn't
       # support the 'aligned' attribute in the way that clang sources requires (for