<rdar://problem/13551789> Fix a race in the LockFileManager.

It's possible for the lock file to disappear and the owning process to
return before we're able to see the generated file. Spin for a little
while to see if it shows up before failing.
[mips] XFAIL test-interp-vec-loadstore.ll in an attempt to turn builder
llvm-mips-linux green.

llvm-mips-linux runs on a big endian machine. This test passes if I change 'e'
to 'E' in the target data layout string.