[gn build] Port 09c266b

Author: llvmgnsyncbot

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

@@ -100,6 +100,7 @@ if (current_toolchain == default_toolchain) {
       "__algorithm/find_segment_if.h",
       "__algorithm/for_each.h",
       "__algorithm/for_each_n.h",
+      "__algorithm/for_each_n_segment.h",
       "__algorithm/for_each_segment.h",
       "__algorithm/generate.h",
       "__algorithm/generate_n.h",