"Hidden" LLVM flags

[Jan Stolarek]

DynFlags list some LLVM flags as "hidden":

  ( "llvm-tbaa",                        Opt_LlvmTBAA, nop), -- hidden flag
  ( "llvm-pass-vectors-in-regs",        Opt_LlvmPassVectorsInRegisters, nop), -- hidden flag

Do I undertsand correctly that "hidden" means "not documented in the User's Guide"? Is there a 
good reason for this? I'd like to document them as part of #9358, especially that -fllvm-tbaa is 
enabled by default for all optimisation levels.

Janek