Disable MSVC's C4702 warning

It flags aes_ctr_set_key as having unreachable code in no-asm builds. It
is true that there is unreachable code in there, but I'm unclear on why
just that function is being flagged. Since we often will no-op our
platform codepaths to avoid ifdefs in build configurations that don't
want them, such a sensitive warning is not useful. Just turn it off.

Fixed: 385161043
Change-Id: I5ed066d6d1d95dcc57a1cac01fad553e9ef4db7d
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/74607
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Auto-Submit: David Benjamin <davidben@google.com>

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d96aad..63efa91 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -188,6 +188,8 @@
       "C4244" # 'function' : conversion from 'int' to 'uint8_t',
               # possible loss of data
       "C4267" # conversion from 'size_t' to 'int', possible loss of data
+      "C4702" # unreachable code; MSVC's warning is too aggressive. See
+              # https://crbug.com/385161043
       "C4706" # assignment within conditional expression
       )
   string(REPLACE "C" " -wd" MSVC_DISABLED_WARNINGS_STR