This works in a similar way to the ELF checks, but uses otool(1) to list the
library name and its dependencies, and the checks fail if there are WRKDIR
references or if the -install_name of the library does not match $PREFIX, as
well as ensuring that any libraries from pkgsrc are correctly registered as
full dependencies.
Removes support for the user to set USE_CHECK_SHLIBS_ELF, but there were no
reasonable reasons for doing so in the past anyway, and it may be masking
issues in platform files we should fix.
f648dfa7c3