[libc] Add an optional `NAME` argument to `add_entrypoint_object` rule.

[sivachandra]

Summary

This argument can be used to specify the entrypoint name if it is different
from the target name.

[abrachet]

libc/cmake/modules/LLVMLibCRules.cmake

113

Name is also optional, should it's comment say so?

[sivachandra]

libc/cmake/modules/LLVMLibCRules.cmake

113

I called them "optional arguments" throughout which is probably a mistake/misnomer. They should actually be called "option arguments" to match the CMake documentation: https://cmake.org/cmake/help/v3.14/command/cmake_parse_arguments.html

Will update separately.

[gchatelet]

LGTM thx!

libc/cmake/modules/LLVMLibCRules.cmake

 
 set(ENTRYPOINT_OBJ_TARGET_TYPE "ENTRYPOINT_OBJ")
 
 # A rule for entrypoint object targets.
 # Usage:
 #     add_entrypoint_object(
 #       <target_name>
 #       [REDIRECTED] # Specified if the entrypoint is redirected.
+#       [NAME] <the C name of the entrypoint if different from target_name>
 #       SRCS <list of .cpp files>
 #       HDRS <list of .h files>
 #       DEPENDS <list of dependencies>
 #     )
 function(add_entrypoint_object target_name)
   cmake_parse_arguments(
     "ADD_ENTRYPOINT_OBJ"
     "REDIRECTED" # Optional argument
-    "" # No single value arguments
+    "NAME" # Single value arguments
     "SRCS;HDRS;DEPENDS"  # Multi value arguments
     ${ARGN}
   )
   if(NOT ADD_ENTRYPOINT_OBJ_SRCS)
     message(FATAL_ERROR "`add_entrypoint_object` rule requires SRCS to be specified.")
   endif()
   if(NOT ADD_ENTRYPOINT_OBJ_HDRS)
     message(FATAL_ERROR "`add_entrypoint_object` rule requires HDRS to be specified.")
   endif()
 
+  set(entrypoint_name ${target_name})
+  if(ADD_ENTRYPOINT_OBJ_NAME)
+    set(entrypoint_name ${ADD_ENTRYPOINT_OBJ_NAME})
+  endif()
+
   add_library(
     "${target_name}_objects"
     # We want an object library as the objects will eventually get packaged into
     # an archive (like libc.a).
     OBJECT
     ${ADD_ENTRYPOINT_OBJ_SRCS}
     ${ADD_ENTRYPOINT_OBJ_HDRS}
   )
function(add_entrypoint_object target_name)
   if(ADD_ENTRYPOINT_OBJ_REDIRECTED)
     set(alias_attributes "${alias_attributes},hidden")
   endif()
 
   add_custom_command(
     OUTPUT ${object_file}
     # We llvm-objcopy here as GNU-binutils objcopy does not support the 'hidden' flag.
     DEPENDS ${object_file_raw} ${llvm-objcopy}
-    COMMAND $<TARGET_FILE:llvm-objcopy> --add-symbol "${target_name}=.llvm.libc.entrypoint.${target_name}:${alias_attributes}" ${object_file_raw} ${object_file}
+    COMMAND $<TARGET_FILE:llvm-objcopy> --add-symbol "${entrypoint_name}=.llvm.libc.entrypoint.${entrypoint_name}:${alias_attributes}" ${object_file_raw} ${object_file}
   )
 
   add_custom_target(
     ${target_name}
     ALL
     DEPENDS ${object_file}
   )
   set_target_properties(