Re: Patch for config.guess for "cross-compiling" x86_64 -> powerpc on Mac OS X <= 10.6

[Bruno Haible]

The patch looks good to me:

  - I confirm that executables built on Mac OS X 10.5.8 (Darwin 9.8.0)
    with "gcc -arch ppc" are of type 'Mach-O executable ppc' and
    are directly executable on x86_64 Mac OS X 10.5.8.

  - This is a vendor-provided feature; I have this feature on x86_64
    Mac OS X 10.5.8 although I haven't installed or configured or
    enabled anything special.
    
  - On a PowerPC Mac OS X 10.5.8 the result of config.guess is
    powerpc-apple-darwin9.8.0, and the patch makes it return the same
    triple for CC="gcc -arch ppc" on x86_64 Mac OS X 10.5.8.

  - The patch is complete: When you compile with "gcc -arch ppc64" you
    get executables of type 'Mach-O 64-bit executable ppc64' but such
    files are not directly executable on x86_64 Mac OS X 10.5.8:
      $ ./a.out
      -bash: ./a.out: Bad CPU type in executable

> The main problem is that config.guess is being used by various
> software packages to answer two completely different questions and the
> answer might not always be the same:
> 
> (1) Which platform am I building for?
> (2) Which platform am I running on / which binaries should I download?

config.guess is the answer for (1). That's why it uses $CC_FOR_BUILD.
For (2) there is no simple answer on bi-arch systems.

Bruno