depends: fix for llvm-ranlib (etc): 'No such file or directory' macOS 15.0
This is an attempt to fix the issue https://github.com/bitcoin/bitcoin/issues/30978 .
To briefly summarize, @Sjors found that while compiling dependencies on macOS 15.0 the following "No such file or directory" are generated while these tools are installed.
$ cd depends
$ make
/bin/sh: command -v llvm-ranlib: No such file or directory
/bin/sh: command -v llvm-strip: No such file or directory
/bin/sh: command -v llvm-nm: No such file or directory
/bin/sh: command -v llvm-objdump: No such file or directory
/bin/sh: command -v dsymutil: No such file or directory
The proposed fix conditionally defines the necessary variables for these tools in the ./depends/Makefile when building on macOS. The rationale is described in more detail in https://github.com/bitcoin/bitcoin/issues/30978#issuecomment-2379782629 as the Solution number 3.
cc @hebasto