Suppress C4701 on 2661 branch.

p256-x86_64.c can't build in MSVC 2013 in debug mode along because of
ecp_nistz256_points_mul's very awkward calling convention (at least one of
g_scalar/p_scalar must be non-NULL).

MSVC 2015 seems to be okay with it, but this branch doesn't build with 2015 yet
and is currently used by gRPC folks. Later they'll move to a branch that builds
with 2015, so the issue won't be pressing. Though the EC_METHOD mul calling
convention is still a little screwy.

The simplest immediate option is to suppress the warning on this branch. The
warning will be left alive on master (which now requires 2015 anyway), but we
should add release-mode builders.

Change-Id: Ia9274887f49dbe8f53c44c046b6f1323425702b0
Reviewed-on: https://boringssl-review.googlesource.com/7987
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8493559..05b6561 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -62,6 +62,7 @@
               # copy constructor is inaccessible or deleted
       "C4626" # assignment operator could not be generated because a base class
               # assignment operator is inaccessible or deleted
+      "C4701" # potentially uninitialized local variable 'p' used
       "C4706" # assignment within conditional expression
       "C4710" # 'function': function not inlined
       "C4711" # function 'function' selected for inline expansion