[BOLT][DWARF] Change to process and write out TUs first then CUs in batches

To reduce memory footprint changed so that we process and write out TUs first,
reset DIEBuilder and process CUs. CUs are processed in buckets. First bucket
contains all the CUs with cross CU references. Rest processd one at a time.

clang-17 build in debug mode, by clang-17.
before
8:25.81 real, 834.37 user, 86.03 sys, 0 amem, 79525064 mmem
8:02.20 real, 820.46 user, 81.81 sys, 0 amem, 79501616 mmem
7:52.69 real, 802.01 user, 83.99 sys, 0 amem, 79534392 mmem

after
7:49.35 real, 822.04 user, 66.19 sys, 0 amem, 34934260 mmem
7:42.16 real, 825.46 user, 63.52 sys, 0 amem, 34951660 mmem
7:46.71 real, 821.11 user, 63.14 sys, 0 amem, 34981164 mmem

Reviewed By: maksfb

Differential Revision: https://reviews.llvm.org/D151909