[mips] Correct linux dynamic linker for -mnan=2008

[dsanders]

Summary

The dynamic linker is named ld-linux-mipsn8.so.1 when -mnan=2008 is given (or
is the default). It remains ld.so.1 for other cases.

This is necessary for MIPS32r6/MIPS64r6 since these ISA's default to -mnan=2008.

[atanasyan]

LGTM with a small note.

lib/Driver/Tools.cpp

5105

As to me I would write this code as follow to escape redundant checking of the -mcpu arguments if -mnan option is provided:

if (Arg *NaNArg = Args.getLastArg(options::OPT_mnan_EQ))
  return llvm::StringSwitch<bool>(NaNArg->getValue())
                .Case("2008", true)
                .Case("legacy", false)
                .Default(false);

// NaN2008 is the default for MIPS32r6/MIPS64r6.
if (Arg *CPUArg = Args.getLastArg(options::OPT_mcpu_EQ))
  return llvm::StringSwitch<bool>(CPUArg->getValue())
                .Cases("mips32r6", "mips64r6", true)
                .Default(false);

return false;

[dsanders]

lib/Driver/Tools.cpp

5105

Good point. I'll change to that before commit

[dsanders]

Make the change suggested by Simon and fix a couple silly mistakes caught by
'ninja check-clang'.