Add Mach-O support to check-shlibs

[Jonathan Perkin <jperkin%joyent.com@localhost>]

Hey all,

This commit adds support for Mach-O executables to our check-shlibs
checks, ensuring that we do not ship packages with broken REQUIRES:

  https://github.com/joyent/pkgsrc/commit/8d8413b

check-shlibs-macho.awk is mostly a copy of check-shlibs-elf.awk but
uses otool(1) to sanitise the list of shared library dependencies.

The commit changes some variables, primarily:

  USE_CHECK_SHLIBS_ELF -> _USE_CHECK_SHLIBS_NATIVE

While this was set up to be a public variable, I think it's highly
unlikely that anyone is using it, and changing it is only masking
broken _OPSYS_CAN_CHECK_SHLIBS settings in platform files which should
be fixed anyway.  If users really want to disable the shlibs checks,
then there is still the documented CHECK_SHLIBS variable.

Prior to this check, some of the packages I've been distributing in
our OSX package sets are broken, e.g.:

  $ pkgin in tdb
  calculating dependencies... done.
  /Users/pbulk/build/databases/tdb/work/tdb-1.3.4/bin/default/libtdb.inst.dylib, needed by tdb-1.3.4 is not present in this system.
  /Users/pbulk/build/databases/tdb/work/tdb-1.3.4/bin/default/libtdb.dylib, needed by tdb-1.3.4 is not present in this system.

  $ pkgin in pev
  calculating dependencies... done.
  libpe.1.0.dylib, needed by pev-0.70 is not present in this system.

This is due to incorrect use of the -install_name argument to the
Darwin linker.  Building those packages with my patch applied
correctly fails the packages at check time, ensuring we do not ship
broken packages:

  $ cd security/pev
  $ bmake _check-shlibs
  => Checking for missing run-time search paths in pev-0.70
  ERROR: bin/ofs2rva: missing library: libpe.1.0.dylib
  ...
  *** Error code 1

  $ cd databases/tdb
  $ bmake _check-shlibs
  => Checking for missing run-time search paths in tdb-1.3.4
  ERROR: lib/libtdb.1.3.4.dylib: path relative to WRKDIR
  *** Error code 1

This has been tested in a full bulk build on SmartOS, and I am in the
process of testing it in a full bulk build on OSX.

Please review.  Thanks!

-- 
Jonathan Perkin  -  Joyent, Inc.  -  www.joyent.com