[libc] Include object files from alias entrypoints also in entrypoint libraries.

[abrachet]

LG to me too

libc/cmake/modules/LLVMLibCLibraryRules.cmake

foreach(dep IN LISTS ARGN)
     get_target_property(indirect_deps ${dep} "DEPS")
     get_object_files_for_entrypoint_library(indirect_objfiles ${indirect_deps})
     list(APPEND object_files ${indirect_objfiles})
   endforeach(dep)
   list(REMOVE_DUPLICATES object_files)
   set(${result} ${object_files} PARENT_SCOPE)
 endfunction()
 
+# This is a helper function and not a build rule. Given an entrypoint object
+# target, it returns the object file produced by this target in |result|.
+# If the given entrypoint target is an alias, then it traverses up to the
+# aliasee to get the object file.
+function(get_entrypoint_object_file entrypoint_target result)
+  get_target_property(target_type ${entrypoint_target} "TARGET_TYPE")
+  if(NOT (${target_type} STREQUAL ${ENTRYPOINT_OBJ_TARGET_TYPE}))
+    message(FATAL_ERROR
+            "Expected an target added using `add_entrypoint_object` rule.")
+  endif()
+
+  get_target_property(objfile ${entrypoint_target} "OBJECT_FILE")
+  if(objfile)
+    set(${result} ${objfile} PARENT_SCOPE)
+    return()
+  endif()
+
+  # If the entrypoint is an alias, fetch the object file from the aliasee.
+  get_target_property(is_alias ${entrypoint_target} "IS_ALIAS")
+  if(is_alias)
+    get_target_property(aliasee ${entrypoint_target} "DEPS")
+    if(NOT aliasee)
+      message(FATAL_ERROR
+              "Entrypoint alias ${entrypoint_target} does not have an aliasee.")
+    endif()
+    get_entrypoint_object_file(${aliasee} objfile)
+    set(${result} ${objfile} PARENT_SCOPE)
+    return()
+  endif()
+
+  message(FATAL_ERROR
+          "Entrypoint ${entrypoint_target} does not produce an object file.")
+endfunction(get_entrypoint_object_file)
+
 # A rule to build a library from a collection of entrypoint objects.
 # Usage:
 #     add_entrypoint_library(
 #       DEPENDS <list of add_entrypoint_object targets>
 #     )
 #
 # NOTE: If one wants an entrypoint to be availabe in a library, then they will
 # have to list the entrypoint target explicitly in the DEPENDS list. Implicit
function(add_entrypoint_library target_name)
   get_fq_deps_list(fq_deps_list ${ENTRYPOINT_LIBRARY_DEPENDS})
   get_object_files_for_entrypoint_library(obj_list ${fq_deps_list})
   foreach(dep IN LISTS fq_deps_list)
     get_target_property(dep_type ${dep} "TARGET_TYPE")
     if(NOT (${dep_type} STREQUAL ${ENTRYPOINT_OBJ_TARGET_TYPE}))
       message(FATAL_ERROR "Dependency '${dep}' of 'add_entrypoint_collection' is "
                           "not an 'add_entrypoint_object' target.")
     endif()
-    get_target_property(objfile ${dep} "OBJECT_FILE")
+    get_entrypoint_object_file(${dep} objfile)
     list(APPEND obj_list ${objfile})
   endforeach(dep)
   list(REMOVE_DUPLICATES obj_list)
 
   set(library_file "${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_STATIC_LIBRARY_PREFIX}${target_name}${CMAKE_STATIC_LIBRARY_SUFFIX}")
   add_custom_command(
     OUTPUT ${library_file}
     COMMAND ${CMAKE_AR} -r ${library_file} ${obj_list}

libc/cmake/modules/LLVMLibCObjectRules.cmake

if(ADD_ENTRYPOINT_OBJ_ALIAS)
     add_custom_target(${fq_target_name})
     add_dependencies(${fq_target_name} ${fq_dep_name})
     get_target_property(object_file ${fq_dep_name} "OBJECT_FILE")
     get_target_property(object_file_raw ${fq_dep_name} "OBJECT_FILE_RAW")
     set_target_properties(
       ${fq_target_name}
       PROPERTIES
         "TARGET_TYPE" ${ENTRYPOINT_OBJ_TARGET_TYPE}
+        "IS_ALIAS" "YES"
         "OBJECT_FILE" ""
         "OBJECT_FILE_RAW" ""
         "DEPS" "${fq_dep_name}"
     )
     return()
   endif()
 
   if(NOT ADD_ENTRYPOINT_OBJ_SRCS)