sal: add aligned memory allocation with malloc for OS X < 10.6

Note that posix_memalign is not available everywhere
(as are its replacements like memalign). For example,
Darwin/OSX <10.6 has neither posix_memalign or memalign.

Incorporating changes by Stephan Bergmann <sbergman@redhat.com>.

Change-Id: I4a02b40c36d353c2b7a78d0bacb3b14e1f2d94da
Reviewed-on: https://gerrit.libreoffice.org/8405
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Stephan Bergmann <sbergman@redhat.com>