[libomptarget] Set runpath on libomptarget, use that to drop LD_LIBRARY_PATH from test runner

[JonChesterfield]

Summary

Using rpath instead of LD_LIBRARY_PATH to find libomp.so and
libomptarget.so lets one rerun the already built test executables without
setting environment variables and removes the risk of the test runner picking
up different libraries to the developer debugging the failure.

rpath usually means runpath, which is not transitive, so set runpath on
libomptarget itself so that it can find the plugins located next to it,
spelled $ORIGIN. This provides sufficient functionality to drop D102043

[grokos]

This solution is quite neat and much simpler than D102043, in line with what we want. LGTM, waiting for other people's opinions.

[tianshilei1992]

This is the right direction for tests. LGTM.

openmp/libomptarget/src/CMakeLists.txt

if(LIBOMP_OMPT_SUPPORT_IN_LIBOMPTARGET)
   list(APPEND LIBOMPTARGET_LLVM_INCLUDE_DIRS ${LIBOMP_INCLUDE_DIR})
 endif()
 
 set(LIBOMPTARGET_SRC_FILES ${LIBOMPTARGET_SRC_FILES} PARENT_SCOPE)
 include_directories(${LIBOMPTARGET_LLVM_INCLUDE_DIRS})
 
 # Build libomptarget library with libdl dependency.
 add_library(omptarget SHARED ${LIBOMPTARGET_SRC_FILES})
+set_target_properties(omptarget PROPERTIES INSTALL_RPATH "$ORIGIN" BUILD_RPATH "$ORIGIN")
 if (OPENMP_ENABLE_LIBOMPTARGET_PROFILING)
   # Add LLVMSupport dependency if profiling is enabled.
   # Linking with LLVM component libraries also requires
   # aligning the compile flags.
   llvm_update_compile_flags(omptarget)
   target_compile_definitions(omptarget PUBLIC OMPTARGET_PROFILE_ENABLED)
   target_link_libraries(omptarget PRIVATE LLVMSupport)
 endif()
 target_link_libraries(omptarget PRIVATE
   ${CMAKE_DL_LIBS}
   "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/exports")
 
 # Install libomptarget under the lib destination folder.
 install(TARGETS omptarget LIBRARY COMPONENT omptarget
   DESTINATION "${OPENMP_INSTALL_LIBDIR}")

openmp/libomptarget/test/lit.cfg

if config.operating_system == 'Windows':
     append_dynamic_library_path('PATH', config.omp_host_rtl_directory, ";")
 elif config.operating_system == 'Darwin':
     append_dynamic_library_path('DYLD_LIBRARY_PATH', config.library_dir, ":")
     append_dynamic_library_path('DYLD_LIBRARY_PATH', \
         config.omp_host_rtl_directory, ";")
     config.test_flags += " -Wl,-rpath," + config.library_dir
     config.test_flags += " -Wl,-rpath," + config.omp_host_rtl_directory
 else: # Unices
-    append_dynamic_library_path('LD_LIBRARY_PATH', config.library_dir, ":")
-    append_dynamic_library_path('LD_LIBRARY_PATH', \
-        config.omp_host_rtl_directory, ":")
+    config.test_flags += " -Wl,-rpath," + config.library_dir
+    config.test_flags += " -Wl,-rpath," + config.omp_host_rtl_directory
     if config.cuda_libdir:
-        append_dynamic_library_path('LD_LIBRARY_PATH', config.cuda_libdir, ":")
+        config.test_flags += " -Wl,-rpath," + config.cuda_libdir
     append_dynamic_library_path('LIBRARY_PATH', config.library_dir, ":")
     append_dynamic_library_path('LIBRARY_PATH', \
         config.omp_host_rtl_directory, ":")
 
 # substitutions
 # - for targets that exist in the system create the actual command.
 # - for valid targets that do not exist in the system, return false, so that the
 #   same test can be used for different targets.