[gn build] Port cedb44a

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -1512,7 +1512,6 @@ if (current_toolchain == default_toolchain) {
       "__memory/array_cookie.h",
       "__memory/assume_aligned.h",
       "__memory/auto_ptr.h",
-      "__memory/builtin_new_allocator.h",
       "__memory/compressed_pair.h",
       "__memory/concepts.h",
       "__memory/construct_at.h",
@@ -1845,6 +1844,7 @@ if (current_toolchain == default_toolchain) {
       "__utility/cmp.h",
       "__utility/convert_to_integral.h",
       "__utility/declval.h",
+      "__utility/element_count.h",
       "__utility/empty.h",
       "__utility/exception_guard.h",
       "__utility/exchange.h",