[gn build] Port 73cd84a

Author: aeubanks

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

@@ -1525,12 +1525,14 @@ if (current_toolchain == default_toolchain) {
       "__fwd/get.h",
       "__fwd/ios.h",
       "__fwd/istream.h",
+      "__fwd/map.h",
       "__fwd/mdspan.h",
       "__fwd/memory.h",
       "__fwd/memory_resource.h",
       "__fwd/ostream.h",
       "__fwd/pair.h",
       "__fwd/queue.h",
+      "__fwd/set.h",
       "__fwd/span.h",
       "__fwd/sstream.h",
       "__fwd/stack.h",