[offload] Copy cmake/DetectTestCompiler from openmp

Copy DetectTestCompiler directory as required
by `cmake/OpenMPTesting.cmake`.

Author: mgorny

offload/cmake/DetectTestCompiler/CMakeLists.txt

@@ -0,0 +1,47 @@
+cmake_minimum_required(VERSION 3.20.0)
+project(DetectTestCompiler C CXX)
+
+include(CheckCCompilerFlag)
+include(CheckCXXCompilerFlag)
+include(CheckIncludeFile)
+include(CheckIncludeFileCXX)
+
+function(write_compiler_information lang)
+  set(information "${CMAKE_${lang}_COMPILER}")
+  set(information "${information}\\;${CMAKE_${lang}_COMPILER_ID}")
+  set(information "${information}\\;${CMAKE_${lang}_COMPILER_VERSION}")
+  set(information "${information}\\;${${lang}_FLAGS}")
+  set(information "${information}\\;${${lang}_HAS_TSAN_FLAG}")
+  set(information "${information}\\;${${lang}_HAS_OMIT_FRAME_POINTER}")
+  set(information "${information}\\;${${lang}_HAS_OMP_H}")
+  file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/${lang}CompilerInformation.txt ${information})
+endfunction(write_compiler_information)
+
+find_package(OpenMP)
+if (NOT OpenMP_Found)
+  set(OpenMP_C_FLAGS "-fopenmp")
+  set(OpenMP_CXX_FLAGS "-fopenmp")
+endif()
+
+set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
+set(THREADS_PREFER_PTHREAD_FLAG TRUE)
+find_package(Threads REQUIRED)
+
+set(C_FLAGS "${OpenMP_C_FLAGS} ${CMAKE_THREAD_LIBS_INIT}")
+set(CXX_FLAGS "${OpenMP_CXX_FLAGS} ${CMAKE_THREAD_LIBS_INIT}")
+
+check_c_compiler_flag("-fno-omit-frame-pointer" C_HAS_OMIT_FRAME_POINTER)
+check_cxx_compiler_flag("-fno-omit-frame-pointer" CXX_HAS_OMIT_FRAME_POINTER)
+
+set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
+set(CMAKE_REQUIRED_FLAGS "-fsanitize=thread")
+check_c_compiler_flag("" C_HAS_TSAN_FLAG)
+check_cxx_compiler_flag("" CXX_HAS_TSAN_FLAG)
+set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
+
+# Check if omp.h header exists for the test compiler
+check_include_file_cxx(omp.h CXX_HAS_OMP_H)
+check_include_file(omp.h C_HAS_OMP_H)
+
+write_compiler_information(C)
+write_compiler_information(CXX)