[gn build] Port 2194bca

Author: llvmgnsyncbot

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

@@ -1061,6 +1061,7 @@ if (current_toolchain == default_toolchain) {
       "__format/indic_conjunct_break_table.h",
       "__format/parser_std_format_spec.h",
       "__format/range_default_formatter.h",
+      "__format/range_format.h",
       "__format/range_formatter.h",
       "__format/unicode.h",
       "__format/width_estimation_table.h",