"make_binary_distribution" does not always generate correct names

Originally, we solved deficiencies of the predefined "autoconf" macros
(at least on OS X 10.5, they do not correctly differ between "x86" and
"x86_64") by providing explicit "--platform" arguments.

With this patch, "make_binary_distribution" evaluates CFLAGS, so it
"just works" because CFLAGS contains information about the target CPU.

This patch is accompanied by a change in our build tools that drops the
setting of "--platform" arguments.

scripts/make_binary_distribution.sh:
  This is a fix for bug#37808
     "make_binary_distribution" does not always generate correct names
  
  Our platform names are the combination of operating system, architecture (CPU),
  and a possible suffix (typically "64bit", if a CPU is available in 32 bit too).
  We get these values from some predefined "autoconf" macros.
  
  However, these macros are not perfect, especially on OS X 10.5 they do not
  differ correctly between x86 (32 bit) and x86_64 (64 bit).
  Originally, we solved that by providing an explicit "--platform" argument,
  but it is better to get rid of that and ensure the script "just works".
  
  The best indication we have about the CPU is the "CFLAGS" value provided
  with "configure" and used in "make": It describes for which CPU the
  binaries are generated, not just which one was running the build.
  This approach should work even if we implement cross-compilation.
  
  So this patch evaluates CFLAGS and extracts its "-arch XYZ" part.
  
  When touching the file, I also replaced some tab characters by blanks.