Enable MSVC warning C4701, use of potentially uninitialized variable.

C4701 is "potentially uninitialized local variable 'buf' used". It
sometimes results in false positives, which can now be suppressed
using the macro OPENSSL_SUPPRESS_POTENTIALLY_UNINITIALIZED_WARNINGS.

Change-Id: I15068b5a48e1c704702e7752982b9ead855e7633
Reviewed-on: https://boringssl-review.googlesource.com/3160
Reviewed-by: Adam Langley <agl@google.com>
9 files changed