Revert "Allow overriding CMAKE_CXX_COMPILER (#436)" (#440)

This reverts commit 5b9907034e.

[ROCm/rocdecode commit: b2149abcef]

projects/rocdecode/samples/videoDecodeBatch/CMakeLists.txt

@@ -36,7 +36,7 @@ endif()
 
 list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/../../cmake)
 list(APPEND CMAKE_PREFIX_PATH ${ROCM_PATH}/hip ${ROCM_PATH})
-set(CMAKE_CXX_COMPILER ${ROCM_PATH}/lib/llvm/bin/clang++ CACHE STRING "ROCm Compiler path")
+set(CMAKE_CXX_COMPILER ${ROCM_PATH}/lib/llvm/bin/clang++)
 
 # rocDecode sample build type
 set(DEFAULT_BUILD_TYPE "Release")