Use cmake's builtin mechanism for handling library locations

See [the documentation](https://cmake.org/cmake/help/v3.0/command/find_package.html)
for exactly how the search procedure works. If you want to use an
LLVM from a specific location, use CMAKE_PREFIX_PATH as normal.

No longer do we have a nonstandard HIPIFY_CLANG_LLVM_DIR variable
for people to learn about.


[ROCm/clr commit: de8dcf0ed2]

projects/clr/hipamd/CMakeLists.txt

@@ -125,13 +125,6 @@ else()
     message(FATAL_ERROR "Don't know where to install HIP. Please specify absolute path using -DCMAKE_INSTALL_PREFIX")
 endif()
 
-# Check if we need to build hipify-clang
-if(NOT DEFINED HIPIFY_CLANG_LLVM_DIR)
-    if(DEFINED ENV{HIPIFY_CLANG_LLVM_DIR})
-        set(HIPIFY_CLANG_LLVM_DIR $ENV{HIPIFY_CLANG_LLVM_DIR})
-    endif()
-endif()
-
 # Check if we need to enable ATP marker
 if(NOT DEFINED COMPILE_HIP_ATP_MARKER)
     if(NOT DEFINED ENV{COMPILE_HIP_ATP_MARKER})

projects/clr/hipamd/hipify-clang/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 2.8.8)
 project(hipify-clang)
 
-find_package(LLVM PATHS ${HIPIFY_CLANG_LLVM_DIR} REQUIRED NO_DEFAULT_PATH)
+find_package(LLVM REQUIRED)
 message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
 
 option(HIPIFY_CLANG_TESTS "Build the tests for hipify-clang, if lit is installed" OFF)