MIPS: Use -G option to specify MIPS section threshold. Translate it

to the -mllvm -mips-ssection-threshold=<value> pair and pass to the frontend.
The patch suggested by Carl Norum.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162697 91177308-0d34-0410-b5e6-96231b3b80d8