[CMake] Remove redundant logic in runtimes/CMakeList.txt

[aoli]

Summary

SUB_CHECK_TARGETS contains all test targets in SUB_COMPONENTS when
we load Components.cmake. We don't need to add those targets
again and having duplicate targets will break the cmake policy CMP0002.

[phosek]

LGTM

runtimes/CMakeLists.txt

if(NOT LLVM_RUNTIME_TARGETS)
           install-${runtime_name})
         if(LLVM_INCLUDE_TESTS)
           list(APPEND test_targets check-${runtime_name})
         endif()
       endforeach()
 
       if(LLVM_INCLUDE_TESTS)
         list(APPEND test_targets runtimes-test-depends check-runtimes)
-        foreach(component ${SUB_COMPONENTS})
-          list(APPEND SUB_CHECK_TARGETS check-${component})
-        endforeach()
       endif()
 
       llvm_ExternalProject_Add(runtimes
                                ${CMAKE_CURRENT_SOURCE_DIR}
                                DEPENDS ${deps}
                                # Builtins were built separately above
                                CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                           -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}