CMake: add C4471 warning as error for MSVC: enum forward declare must have underlying type

Bug: b/131224705
Change-Id: I7f971cd72ab623ba3798231b8b2a1b77e7744f78
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31369
Presubmit-Ready: Antonio Maiorano <amaiorano@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 091fbd0..9585f9c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -256,6 +256,7 @@
     # Treat specific warnings as errors
     list(APPEND SWIFTSHADER_COMPILE_OPTIONS
         "/we4018" # 'expression' : signed/unsigned mismatch
+        "/we4471" # 'enumeration': a forward declaration of an unscoped enumeration must have an underlying type (int assumed)
         "/we4838" # conversion from 'type_1' to 'type_2' requires a narrowing conversion
         "/we5038" # data member 'member1' will be initialized after data member 'member2' data member 'member' will be initialized after base class 'base_class'
     )