CMake: require version 3.13

A future change will make use of target_link_options, which was added in
CMake 3.13.

Bug: b/145758253
Change-Id: Icac9609c5d2a9df6039a1d3defeb8db9d3cfd61d
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/44109
Tested-by: Antonio Maiorano <amaiorano@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 792ac8c..fd1179d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-cmake_minimum_required(VERSION 3.6.3)
+cmake_minimum_required(VERSION 3.13)
 
 set(CMAKE_CXX_STANDARD 14)