re-fix do/@INC issue in Time-HiRes's Makefile.PL

re-fix do/@INC issue in Time-HiRes's Makefile.PL

Time-HiRes's Makefile.PL loads its hints file using do-file, and so
has needed to be updated for the removal of the implicit "." from @INC.
Commit 8b69401c2ba8d1ced2e17c24d6b51a7ce3882664 attempted to do this,
but put the explicit "." in the input to File::Spec->catfile, which
edits it back out.  Commit ba570843add681d44ff50ff219d1ce000a961663
fixed this problem, by moving the explicit "." into a string
concatenation after File::Spec->catfile has done its bit.  But commit
5cd155b07ed261125793850e101ebe6fa438c5e3 then reverted that fix,
apparently by mistake during preparation for a CPAN release.  This commit
reinstates the fix.