build: swap otool for (llvm-)objdump
Summary:
Similar to libtool, (llvm-)otool only exists with a version suffix on some systems (Ubuntu), which makes it annoying to use/find. Avoid this, by switching to objdump. Which is a drop-in replacement. This is related to #21778, and the switchover to using vanilla LLVM for macOS.
Backport of core#29739.
Depends on D17258.
Test Plan: Run the GUIX osx build
Reviewers: #bitcoin_abc, PiRK
Reviewed By: #bitcoin_abc, PiRK
Subscribers: PiRK
Differential Revision: https://reviews.bitcoinabc.org/D17259