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>
diff --git a/util/generate_build_files.py b/util/generate_build_files.py
index 9d71498..7341a2f 100644
--- a/util/generate_build_files.py
+++ b/util/generate_build_files.py
@@ -428,7 +428,7 @@
 
 # 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)