HIP: Store CMAKE_HIP_HOST_COMPILER as an absolute path

Modules/CMakeDetermineHIPCompiler.cmake

diff --git a/Modules/CMakeDetermineHIPCompiler.cmake b/Modules/CMakeDetermineHIPCompiler.cmake
index a331715..13ec392 100644
--- a/Modules/CMakeDetermineHIPCompiler.cmake
+++ b/Modules/CMakeDetermineHIPCompiler.cmake
@@ -113,6 +113,29 @@
       if(NOT EXISTS "${CMAKE_HIP_HOST_COMPILER}")
         message(FATAL_ERROR "Could not find compiler set in environment variable HIPHOSTCXX:\n$ENV{HIPHOSTCXX}.\n${CMAKE_HIP_HOST_COMPILER}")
       endif()
+    elseif(CMAKE_HIP_HOST_COMPILER)
+      # We get here if CMAKE_HIP_HOST_COMPILER was specified by the user or toolchain file.
+      if(IS_ABSOLUTE "${CMAKE_HIP_HOST_COMPILER}")
+        # Convert to forward slashes.
+        cmake_path(CONVERT "${CMAKE_HIP_HOST_COMPILER}" TO_CMAKE_PATH_LIST CMAKE_HIP_HOST_COMPILER NORMALIZE)
+      else()
+        # Convert to absolute path so changes in `PATH` do not impact HIP compilation.
+        find_program(_CMAKE_HIP_HOST_COMPILER_PATH NO_CACHE NAMES "${CMAKE_HIP_HOST_COMPILER}")
+        if(_CMAKE_HIP_HOST_COMPILER_PATH)
+          set(CMAKE_HIP_HOST_COMPILER "${_CMAKE_HIP_HOST_COMPILER_PATH}")
+        endif()
+        unset(_CMAKE_HIP_HOST_COMPILER_PATH)
+      endif()
+      if(NOT EXISTS "${CMAKE_HIP_HOST_COMPILER}")
+        message(FATAL_ERROR "Could not find compiler set in variable CMAKE_HIP_HOST_COMPILER:\n  ${CMAKE_HIP_HOST_COMPILER}")
+      endif()
+      # If the value was cached, update the cache entry with our modifications.
+      get_property(_CMAKE_HIP_HOST_COMPILER_CACHED CACHE CMAKE_HIP_HOST_COMPILER PROPERTY TYPE)
+      if(_CMAKE_HIP_HOST_COMPILER_CACHED)
+        set_property(CACHE CMAKE_HIP_HOST_COMPILER PROPERTY VALUE "${CMAKE_HIP_HOST_COMPILER}")
+        mark_as_advanced(CMAKE_HIP_HOST_COMPILER)
+      endif()
+      unset(_CMAKE_HIP_HOST_COMPILER_CACHED)
     endif()
   endif()