[gn build] Port 04f01a2

Author: nico

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

@@ -289,7 +289,6 @@ if (current_toolchain == default_toolchain) {
       "__atomic/kill_dependency.h",
       "__atomic/memory_order.h",
       "__atomic/to_gcc_order.h",
-      "__availability",
       "__bit/bit_cast.h",
       "__bit/bit_ceil.h",
       "__bit/bit_floor.h",
@@ -385,7 +384,9 @@ if (current_toolchain == default_toolchain) {
       "__condition_variable/condition_variable.h",
       "__config",
       "__configuration/abi.h",
+      "__configuration/availability.h",
       "__configuration/compiler.h",
+      "__configuration/language.h",
       "__configuration/platform.h",
       "__coroutine/coroutine_handle.h",
       "__coroutine/coroutine_traits.h",