Disable MSVC warning 4065

Warning for a switch statement with 'default' but no 'case labels.
This warning is triggered in the ANGLE CQ and blocking a sws roll.

Bug: angleproject:4299
Change-Id: Id8d98c124e19b6a6834beb9a643b182e2d5876e7
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40248
Tested-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index a32cf80..eba6788 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -55,6 +55,7 @@
     # Diable some MSVC warnings.
     if (!is_clang) {
       cflags += [
+        "/wd4065", # switch statement contains 'default' but no 'case' labels
         "/wd4309", # Truncation of constant value. See PixelRoutine.cpp casts of signed shorts.
       ]
     }