Correct preferred llvm version in CMakeList.txt (#298)

Author: fzou1

CMakeLists.txt

@@ -20,7 +20,7 @@ if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
     add_definitions(-DUSE_PREBUILT_LLVM)
 
     if(NOT PREFERRED_LLVM_VERSION)
-        set(PREFERRED_LLVM_VERSION "12.0.0")
+        set(PREFERRED_LLVM_VERSION "13.0.0")
     endif(NOT PREFERRED_LLVM_VERSION)
     message(STATUS "[OPENCL-CLANG] Looking for LLVM version ${PREFERRED_LLVM_VERSION}")
     find_package(LLVM ${PREFERRED_LLVM_VERSION} REQUIRED)