[mips] Fix >80-column line


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220564 91177308-0d34-0410-b5e6-96231b3b80d8
These functions are not actually defined for NDEBUG or !LLVM_DUMP_ENABLED, so guarding the declarations as well. NFC, silences MSVC warnings in release builds.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220565 91177308-0d34-0410-b5e6-96231b3b80d8