[CMake] Update to retiring CMake 3.4.3

[beanz]

Summary

This is as per the discussions on developer lists:

http://lists.llvm.org/pipermail/llvm-dev/2016-April/098780.html
http://lists.llvm.org/pipermail/llvm-dev/2016-May/100058.html

compiler-rt/trunk/CMakeLists.txt

 # Check if compiler-rt is built as a standalone project.
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(CompilerRT C CXX ASM)
   set(COMPILER_RT_STANDALONE_BUILD TRUE)
 else()
   set(COMPILER_RT_STANDALONE_BUILD FALSE)
 endif()
 
-# The CompilerRT build system requires CMake version 2.8.8 or higher in order
-# to use its support for building convenience "libraries" as a collection of
-# .o files. This is particularly useful in producing larger, more complex
-# runtime libraries.
-if (NOT MSVC)
-  cmake_minimum_required(VERSION 2.8.8)
-else()
-  # Version 2.8.12.1 is required to build with Visual Studio 2013.
-  cmake_minimum_required(VERSION 2.8.12.1)
-endif()
+cmake_minimum_required(VERSION 3.4.3)
 
 # FIXME: It may be removed when we use 2.8.12.
 if(CMAKE_VERSION VERSION_LESS 2.8.12)
   # Invalidate a couple of keywords.
   set(cmake_2_8_12_INTERFACE)
   set(cmake_2_8_12_PRIVATE)
   if(APPLE)
     set(CMAKE_MACOSX_RPATH On)

compiler-rt/trunk/lib/builtins/CMakeLists.txt

 # This directory contains a large amount of C code which provides
 # generic implementations of the core runtime library along with optimized
 # architecture-specific code in various subdirectories.
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
-  cmake_minimum_required(VERSION 2.8.12.1)
+  cmake_minimum_required(VERSION 3.4.3)
 
   project(CompilerRTBuiltins C ASM)
   set(COMPILER_RT_STANDALONE_BUILD TRUE)
   set(COMPILER_RT_BUILTINS_STANDALONE_BUILD TRUE)
   list(INSERT CMAKE_MODULE_PATH 0
     "${CMAKE_SOURCE_DIR}/../../cmake"
     "${CMAKE_SOURCE_DIR}/../../cmake/Modules")
   include(base-config-ix)