[lld-macho] Don't sort map file entries by name

ld64 emits them in address order but not in alphabetical order. This
sorting is particularly expensive for dead-stripped symbols (which don't
need to be sorted at all, unlike live symbols that need to be sorted by
address).

Timings for chromium_framework_less_dwarf (with the `-map` flag added to
the response file) on my 16-core Mac Pro:

             base           diff           difference (95% CI)
  sys_time   1.997 ± 0.038  2.004 ± 0.028  [  -0.6% ..   +1.3%]
  user_time  8.698 ± 0.085  8.167 ± 0.070  [  -6.6% ..   -5.6%]
  wall_time  7.965 ± 0.114  7.715 ± 0.347  [  -5.1% ..   -1.2%]
  samples    25             23

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D136536