Fix remaining mips build issues.
Fix remaining mips build issues.

Missed a few things in mutex.cc.

Change-Id: I1c3acfc5faa2511490170199c03ab74c1f23022a

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst