Call skolemize_late_bound_regions only after fast rejection

skolemize_late_bound_regions essentially copies the entire type (most of the times it shouldn't, but it does), and match_impl runs millions of times.

Times compiling rustc, tested with
$ make -j4 rustc-stage1
$ ( time RUSTFLAGS=-Z time-passes make -j4 rustc-stage2 ) # need LLVM time for calibration

Before:
real	21m44.960s
user	29m38.812s
sys	0m14.944s

After:
real	19m31.445s
user	26m47.260s
sys	0m14.952s

Making this is a 10% performance improvement.

LLVM passes took 867 seconds before, 862 seconds after.

0 files changed, 0 insertions, 0 deletions