[ELF][MIPS] Handle section symbol points to the .MIPS.options / .reginfo section

MIPS .reginfo and .MIPS.options sections are consumed by the linker, and
the linker produces a single output section. But it is possible that
input files contain section symbol points to the corresponding input
section. In case of generation a relocatable output we need to write
such symbols to the output file.

Fixes bug 27878.

Differential Revision: http://reviews.llvm.org/D20688

llvm-svn: 270910