[mips] Correct r206370 to account for non-Linux targets using the small data section.

[mips] Correct r206370 to account for non-Linux targets using the small data section.

This should fix the ninja-x64-msvc-RA-centos6 builder.

I suspect the check in MipsSubtarget.cpp is incorrect and is really trying to
check for a bare-metal target rather and anything other than linux. I'll
investigate this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206385 91177308-0d34-0410-b5e6-96231b3b80d8