[gn build] Port c292b60

Author: llvmgnsyncbot

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

@@ -347,6 +347,7 @@ if (current_toolchain == default_toolchain) {
       "__memory/allocator.h",
       "__memory/allocator_arg_t.h",
       "__memory/allocator_traits.h",
+      "__memory/assume_aligned.h",
       "__memory/auto_ptr.h",
       "__memory/compressed_pair.h",
       "__memory/concepts.h",