suse-bzip2/Makefile: add Mac OS X support

suse-bzip2/Makefile: add Mac OS X support

This commit changes the  suse-bzip2 Makefile to compile a dynamic
libbz2.dylib on Mac OS X and ensures that zgz sets DYLD_LIBRARY_PATH
on Mac OS X to swap in a different library.

The suse-bzip2 Makefile was only able to handle the compilation of
shared object libraries like they are used on Linux. Mac OS X uses
dynamic libraries, which require different compiler and linker switches.

MacPorts checks all binaries installed by a port for broken linkage.
This requires that the install_name for libbz2 is set in the suse-bzip2
Makefile to its pristine-tar install location (based on PREFIX).

Signed-off-by: Philipp A. Hartmann <philipp.hartmann@offis.de>
(cherry picked from commit 295dda0608a979d11b7acfb565745b7f507a27a1)