[libc] Correctly pass the C++ standard to NVPTX internal builds

Summary:
The NVPTX build wasn't getting the `C++20` standard necessary for a few
files.

Author: jhuber6

libc/cmake/modules/LLVMLibCObjectRules.cmake

@@ -44,6 +44,10 @@ function(create_object_library fq_target_name)
     message(FATAL_ERROR "'add_object_library' rule requires SRCS to be specified.")
   endif()
 
+  if(NOT ADD_OBJECT_CXX_STANDARD)
+    set(ADD_OBJECT_CXX_STANDARD ${CMAKE_CXX_STANDARD})
+  endif()
+
   set(internal_target_name ${fq_target_name}.__internal__)
   set(public_packaging_for_internal "-DLIBC_COPT_PUBLIC_PACKAGING")
 
@@ -75,6 +79,9 @@ function(create_object_library fq_target_name)
     target_include_directories(${internal_target_name} PRIVATE ${LIBC_SOURCE_DIR})
     target_compile_options(${internal_target_name} PRIVATE ${compile_options}
                            -fno-lto -march=${LIBC_GPU_TARGET_ARCHITECTURE})
+    set_target_properties(${internal_target_name}
+                          PROPERTIES
+                          CXX_STANDARD ${ADD_OBJECT_CXX_STANDARD})
   endif()
 
   if(SHOW_INTERMEDIATE_OBJECTS)
@@ -92,9 +99,6 @@ function(create_object_library fq_target_name)
     target_link_libraries(${fq_target_name} PUBLIC ${fq_deps_list})
   endif()
 
-  if(NOT ADD_OBJECT_CXX_STANDARD)
-    set(ADD_OBJECT_CXX_STANDARD ${CMAKE_CXX_STANDARD})
-  endif()
   set_target_properties(
     ${fq_target_name}
     PROPERTIES