Align CMake requirements with upstream. (#3928)

Author: bader

llvm/CMakeLists.txt

@@ -1,6 +1,6 @@
 # See docs/CMake.html for instructions about how to build LLVM with CMake.
 
-cmake_minimum_required(VERSION 3.14)
+cmake_minimum_required(VERSION 3.13.4)
 
 # CMP0116: Ninja generators transform `DEPFILE`s from `add_custom_command()`
 # New in CMake 3.20. https://cmake.org/cmake/help/latest/policy/CMP0116.html

llvm/lib/SYCLLowerIR/CMakeLists.txt

@@ -1,3 +1,13 @@
+if(${CMAKE_VERSION} VERSION_LESS 3.14)
+    macro(FetchContent_MakeAvailable NAME)
+        FetchContent_GetProperties(${NAME})
+        if(NOT ${NAME}_POPULATED)
+            FetchContent_Populate(${NAME})
+            add_subdirectory(${${NAME}_SOURCE_DIR} ${${NAME}_BINARY_DIR})
+        endif()
+    endmacro()
+endif()
+
 # Lowering of SYCL ESIMD kernels depends on vc-intrinsics
 # NOTE: could have been added earlier from llvm/projects
 if (NOT TARGET LLVMGenXIntrinsics)