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

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.

Differential Revision: http://reviews.llvm.org/D4273

llvm-svn: 211598