[Mips] Follow-up to r179481. Consider "single-float" as a separate
independent of float ABI feature in the MipsTargetInfoBase class.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179486 91177308-0d34-0410-b5e6-96231b3b80d8
[Mips] Follow-up to r179481. Reduce code duplication. Use
AddTargetFeature() routine to handle -msingle-float / -mdouble-float
options.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179487 91177308-0d34-0410-b5e6-96231b3b80d8
[Mips] Fix indentation.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179488 91177308-0d34-0410-b5e6-96231b3b80d8