Update build-tools to ab/4051621

Bug fixes for header-abi-dumper, header-abi-linker and header-abi-diff.

Add merge-abi-diff for post-processing of abi-diff reports.

Test: make -j64

Bug: 32750600

Bug: 38325544

Bug: 38325929

Merged-In: I69a478b8e7a95aeae1dac897337d7636a8f2a05b
Change-Id: I77ad06292eff9c2cf174d774ed1c844d38adf062