[LSan][MIPS64] Enable LSan testing for mips64/mips64el

Patch by Sagar Thakur

Reviewers: petarj, earthdok, kcc.

Subscribers:  samsonov, dsanders, mohit.bhakkad, Anand.Takale, llvm-commits.

Differential Revision: http://reviews.llvm.org/D7124

llvm-svn: 229833