make fails when following the instruction

Instruction mention to define OPENCL_ICD_LOADER_HEADERS_DIR to include header and has no effect so fails. Please test before publishing, otherwise it is useless.
root@sriov-guest:/git.co/khronos# env | grep OPENCL
OPENCL_ICD_LOADER_HEADERS_DIR=/git.co/khronos/OpenCL-Headers/CL/
root@sriov-guest:/git.co/khronos# cd OpenCL-ICD-Loader/
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader# pwd
/git.co/khronos/OpenCL-ICD-Loader
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader# ls
CL CMakeLists.txt CODE_OF_CONDUCT.md LICENSE README.md build inc loader test
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader# cd build
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader/build# cmake ..
-- Configuring done
-- Generating done
-- Build files have been written to: /git.co/khronos/OpenCL-ICD-Loader/build
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader/build# make
[ 20%] Built target OpenCL
[ 24%] Building C object test/log/CMakeFiles/IcdLog.dir/icd_test_log.c.o
/git.co/khronos/OpenCL-ICD-Loader/test/log/icd_test_log.c:5:9: fatal error: CL/cl.h: No such file or directory
#include
^~~~~~~~~
compilation terminated.
test/log/CMakeFiles/IcdLog.dir/build.make:62: recipe for target 'test/log/CMakeFiles/IcdLog.dir/icd_test_log.c.o' failed
make[2]: *** [test/log/CMakeFiles/IcdLog.dir/icd_test_log.c.o] Error 1
CMakeFiles/Makefile2:1042: recipe for target 'test/log/CMakeFiles/IcdLog.dir/all' failed
make[1]: *** [test/log/CMakeFiles/IcdLog.dir/all] Error 2
Makefile:140: recipe for target 'all' failed
make: *** [all] Error 2
root@sriov-guest:/git.co/khronos/OpenCL-ICD-Loader/build#

Start with the build instruction in README.md, then inspect CMakeLists.txt and the test/log target that fails in test/log/icd_test_log.c. Reproduce the reported cmake and make commands with OPENCL_ICD_LOADER_HEADERS_DIR set, and verify that the documented setup builds the test targets successfully.

Written by the indexing model from the issue text.