[compiler-rt][bultins] Fix libatomic standalone build

[phosek]

LGTM

compiler-rt/lib/builtins/CMakeLists.txt

869–870

This can be removed.

883

Since this will only ever be set to builtins, can we just hardcode it here?

[abrachet]

Comments addressed in commit

compiler-rt/lib/builtins/CMakeLists.txt

 endif ()
 
 option(COMPILER_RT_BUILD_STANDALONE_LIBATOMIC
   "Build standalone shared atomic library."
   OFF)
 
 if(COMPILER_RT_BUILD_STANDALONE_LIBATOMIC)
   add_custom_target(builtins-standalone-atomic)
-  set(BUILTIN_DEPS "")
   set(BUILTIN_TYPE SHARED)
   if(${CMAKE_SYSTEM_NAME} MATCHES "AIX")
     if(NOT COMPILER_RT_LIBATOMIC_LINK_FLAGS)
       get_aix_libatomic_default_link_flags(COMPILER_RT_LIBATOMIC_LINK_FLAGS
         "${CMAKE_CURRENT_SOURCE_DIR}/ppc/atomic.exp")
     endif()
-    # The compiler needs builtins to link any other binaries, so let
-    # clang_rt.atomic be built after builtins.
-    set(BUILTIN_DEPS builtins)
     # For different versions of cmake, SHARED behaves differently. For some
     # versions, we might need MODULE rather than SHARED.
     get_aix_libatomic_type(BUILTIN_TYPE)
+  else()
+    list(APPEND COMPILER_RT_LIBATOMIC_LINK_FLAGS -nodefaultlibs)
   endif()
   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
     if(CAN_TARGET_${arch})
       add_compiler_rt_runtime(clang_rt.atomic
                               ${BUILTIN_TYPE}
                               ARCHS ${arch}
                               SOURCES atomic.c
                               LINK_FLAGS ${COMPILER_RT_LIBATOMIC_LINK_FLAGS}
-                              DEPS ${BUILTIN_DEPS}
+                              DEPS builtins
                               PARENT_TARGET builtins-standalone-atomic)
     endif()
   endforeach()
   # FIXME: On AIX, we have to archive built shared libraries into a static
   # archive, i.e., libatomic.a. Once cmake adds support of such usage for AIX,
   # this ad-hoc part can be removed.
   if(${CMAKE_SYSTEM_NAME} MATCHES "AIX")
     archive_aix_libatomic(clang_rt.atomic libatomic
                           ARCHS ${BUILTIN_SUPPORTED_ARCH}
                           PARENT_TARGET builtins-standalone-atomic)
   endif()
   add_dependencies(compiler-rt builtins-standalone-atomic)
 endif()
 
 add_dependencies(compiler-rt builtins)