Bump minimum CMake version.

CMake 3.5.0 was released March 8, 2016. Per our five year rule, we
can require that now:
https://cmake.org/pipermail/cmake/2016-March/062947.html

Change-Id: I916fdb66e0356e3a8ffbe1e5fa89f51d99a78546
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/46345
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

BUILDING.md

@@ -10,7 +10,7 @@ Unless otherwise noted, build tools must at most five years old, matching
 [Abseil guidelines](https://abseil.io/about/compatibility). If in doubt, use the
 most recent stable version of each tool.
 
-  * [CMake](https://cmake.org/download/) 3.0 or later is required.
+  * [CMake](https://cmake.org/download/) 3.5 or later is required.
 
   * A recent version of Perl is required. On Windows,
     [Active State Perl](http://www.activestate.com/activeperl/) has been

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.3)
+cmake_minimum_required(VERSION 3.5)
 
 # Defer enabling C and CXX languages.
 project(BoringSSL NONE)

util/generate_build_files.py

@@ -428,7 +428,7 @@ R'''# Copyright (c) 2019 The Chromium Authors. All rights reserved.
 
 # This file is created by generate_build_files.py. Do not edit manually.
 
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.5)
 
 project(BoringSSL LANGUAGES C CXX)