[mlri][ExecutionEngine] Don't globaly set CMake prefixes to find HIP

[krzysz00]

Summary

The HIP CMake files expect to find their own dependencies and don't
use or respect PATHS or HINTS, relying on CMAKE_PREFIX_PATH to contain
/opt/rocm and /opt/rocm/hip . This is not great for the rest of the
build. Therefore, copy the CMake prefix path, add the ROCm
directories, find HIP, and reset the path to its old value.

[arsenm]

It would be more productive to fix the rocm cmake huild if you’re going to touch this. Not respecting paths or hints is very broken

[krzysz00]

@arsenm That being said, would this make the hack more acceptable since now loading in hip doesn't pollute the global CMake context?

(I don't even know how to start trying to change ROCm's cmake files)

[arsenm]

I guess this is improving things technically

mlir/lib/ExecutionEngine/CMakeLists.txt

if(MLIR_ENABLE_ROCM_RUNNER)
   # Configure ROCm support.
   if (NOT DEFINED ROCM_PATH)
     if (NOT DEFINED ENV{ROCM_PATH})
       set(ROCM_PATH "/opt/rocm" CACHE PATH "Path to which ROCm has been installed")
     else()
       set(ROCM_PATH $ENV{ROCM_PATH} CACHE PATH "Path to which ROCm has been installed")
     endif()
   endif()
+  # A lot of the ROCm CMake files expect to find their own dependencies in
+  # CMAKE_PREFIX_PATH and don't respect PATHS or HINTS :( .
+  # Therefore, temporarily add the ROCm path to CMAKE_PREFIX_PATH so we can
+  # load HIP, then remove it
+  set(REAL_CMAKE_PREFIX_PATH "${CMAKE_PREFIX_PATH}")
   list(APPEND CMAKE_PREFIX_PATH ${ROCM_PATH} "${ROCM_PATH}/hip")
   find_package(hip REQUIRED)
+  set(CMAKE_PREFIX_PATH "${REAL_CMAKE_PREFIX_PATH}")
 
   if (NOT DEFINED ROCM_TEST_CHIPSET)
     execute_process(COMMAND "${ROCM_PATH}/bin/rocm_agent_enumerator"
     OUTPUT_VARIABLE AGENTS_STRING
     ERROR_VARIABLE AGENTS_STRING
     RESULT_VARIABLE AGENT_ENUMERATOR_RESULT)
 
     if (NOT AGENT_ENUMERATOR_RESULT EQUAL 0)