[gn build] Port 89a7bdb

Author: llvmgnsyncbot

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

@@ -192,9 +192,11 @@ if (current_toolchain == default_toolchain) {
       "__functional/binary_function.h",
       "__functional/binary_negate.h",
       "__functional/bind.h",
+      "__functional/bind_back.h",
       "__functional/bind_front.h",
       "__functional/binder1st.h",
       "__functional/binder2nd.h",
+      "__functional/compose.h",
       "__functional/default_searcher.h",
       "__functional/function.h",
       "__functional/hash.h",