Update cmake minimum required to version 3.5

CMakeLists.txt

@@ -1,7 +1,7 @@
 # CMake setup for Unicorn 2.
 # By Huitao Chen & Nguyen Anh Quynh, 2019-2020
 
-cmake_minimum_required(VERSION 3.1)
+cmake_minimum_required(VERSION 3.5)
 
 # Only required for MSVC, but we can't know the compiler at this point because we haven't
 # called enable_language() or project(), and if we did that it would lock in the old
@@ -17,10 +17,8 @@ if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.15")
     cmake_policy(SET CMP0092 NEW)
 endif()
 
-if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.3")
-    # Honor visibility properties for all target types.
-    cmake_policy(SET CMP0063 NEW)
-endif()
+# Honor visibility properties for all target types.
+cmake_policy(SET CMP0063 NEW)
 
 option(ZIG_BUILD "Enable zig build" OFF)
 if(ZIG_BUILD)