We no longer rely on HIPIFY_CLANG_LLVM_DIR to disable hipify-clang

Since there's now an option for toggling hipify-clang, omitting the
path is no longer something we need to check for. We'll still
abort if LLVM isn't found, due to `REQUIRED`.

hipify-clang/CMakeLists.txt

@@ -1,12 +1,7 @@
 cmake_minimum_required(VERSION 2.8.8)
 project(hipify-clang)
 
-if (HIPIFY_CLANG_LLVM_DIR)
-    find_package(LLVM PATHS ${HIPIFY_CLANG_LLVM_DIR} REQUIRED NO_DEFAULT_PATH)
-else()
-    message(STATUS "hipify-clang will not be built. To build it please specify absolute path to LLVM 3.8 or higher using HIPIFY_CLANG_LLVM_DIR")
-    return()
-endif()
+find_package(LLVM PATHS ${HIPIFY_CLANG_LLVM_DIR} REQUIRED NO_DEFAULT_PATH)
 
 option(HIPIFY_CLANG_TESTS "Build the tests for hipify-clang, if lit is installed" OFF)