[XRay][compiler-rt] Use `SANITIZER_CXX_ABI_LIBRARY` for XRay unit tests

[dberris]

Summary

Fix a TODO in CMake config for XRay tests to use the detected C++ ABI
library in the tests.

Also make the tests depend on the llvm-xray target when built in-tree.

compiler-rt/lib/xray/tests/CMakeLists.txt

else()
     set(tgt_name "RTXRay.test.${arch}")
   endif()
   set(${lib} "${tgt_name}" PARENT_SCOPE)
 endfunction()
 
 set(XRAY_TEST_ARCH ${XRAY_SUPPORTED_ARCH})
 set(XRAY_UNITTEST_LINK_FLAGS
   ${CMAKE_THREAD_LIBS_INIT}
+  -l${SANITIZER_CXX_ABI_LIBRARY}
   -fxray-instrument
-  -lstdc++  # TODO: Detect the correct standard library used!
   )
 if (NOT APPLE)
   append_list_if(COMPILER_RT_HAS_LIBM -lm XRAY_UNITTEST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBRT -lrt XRAY_UNITTEST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBDL -ldl XRAY_UNITTEST_LINK_FLAGS)
   append_list_if(COMPILER_RT_HAS_LIBPTHREAD -pthread XRAY_UNITTEST_LINK_FLAGS)
 endif()
 
 macro(add_xray_unittest testname)
   cmake_parse_arguments(TEST "" "" "SOURCES;HEADERS" ${ARGN})
   if(UNIX AND NOT APPLE)
     set(CMAKE_DL_LIBS_INIT "")
     foreach(arch ${XRAY_TEST_ARCH})
       set(TEST_OBJECTS)
       get_xray_lib_for_arch(${arch} XRAY_RUNTIME_LIBS)
       generate_compiler_rt_tests(TEST_OBJECTS
         XRayUnitTests "${testname}-${arch}-Test" "${arch}"
         SOURCES ${TEST_SOURCES} ${COMPILER_RT_GTEST_SOURCE}
         # Note that any change in the implementations will cause all the unit
         # tests to be re-built. This is by design, but may be cumbersome during
         # the build/test cycle.
         COMPILE_DEPS ${TEST_SOURCES} ${COMPILER_RT_GTEST_SOURCE}
         ${XRAY_HEADERS} ${XRAY_ALL_SOURCE_FILES_ABS_PATHS}
         RUNTIME "${XRAY_RUNTIME_LIBS}"
-        DEPS gtest xray
+        DEPS gtest xray llvm-xray
         CFLAGS ${XRAY_UNITTEST_CFLAGS}
         LINK_FLAGS ${TARGET_LINK_FLAGS} ${XRAY_UNITTEST_LINK_FLAGS})
       set_target_properties(XRayUnitTests
         PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
     endforeach()
   endif()
 endmacro()