[ELF] - Do not produce broken .dynamic section with --no-rosegment

LLD produces broken .dynamic section when --no-rosegment and at least
one of following options is present:
  1) -z rodynamic is given.
  2) MIPS target.

That happens because code that writes .dynamic assumes target buffer
is zero-filled, what can be not true after LLD fills it with trap
instructions. With one of two options above, .dynamic becomes
SHF_ALLOC section, so can be affected.

Differential revision: https://reviews.llvm.org/D38580

llvm-svn: 315054