[gn build] Port df324bb

Author: llvmgnsyncbot

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

@@ -286,6 +286,7 @@ if (current_toolchain == default_toolchain) {
       "__ranges/enable_borrowed_range.h",
       "__ranges/enable_view.h",
       "__ranges/iota_view.h",
+      "__ranges/join_view.h",
       "__ranges/non_propagating_cache.h",
       "__ranges/ref_view.h",
       "__ranges/reverse_view.h",