[PATCH] Make Mach-O autoconf Check Cacheable Variable

[[[
Make the Mach-O check an autoconf cacheable variable
* build/ac-macros/macosx.m4
   (SVN_LIB_MACHO_ITERATE): Wrapped the m4 macro inside an AC_CACHE_CHECK;
this allows
   the result of the check to passed 'configure' explicitly, eliminating the
need to compile and run
   a test program. This is necessary when cross-compiling to a different
architecture because
   the test program is also cross-compiled and won't run in the host
environment.
]]]