export-file-local-symbols: include in help output

goto-cc --export-file-local-symbols was never documented in --help
output.

Author: tautschnig

src/goto-cc/goto_cc_mode.cpp

@@ -64,6 +64,9 @@ void goto_cc_modet::help()
   " --native-compiler cmd       command to invoke as preprocessor/compiler\n"
   " --native-linker cmd         command to invoke as linker\n"
   " --native-assembler cmd      command to invoke as assembler (goto-as only)\n"
+  " --export-file-local-symbols\n"
+  "                             name-mangle and export file-local symbols\n"
+  " --mangle-suffix suffix      append suffix to exported file-local symbols\n"
   " --print-rejected-preprocessed-source file\n"
   "                             copy failing (preprocessed) source to file\n"
   " --object-bits               number of bits used for object addresses\n"