How to build fat gcc46 libstdc++ on OS X?

Question

I have successfully built and installed gcc 4.6.1 on my OS X box, but I can't seem to get it to create a fat/universal libstdc++ library for me. How do I make it do that?

The default /usr/lib/libstdc++.6.dylib supports the following architectures:

[host:~] nsteiner% file /usr/lib/libstdc++.6.dylib
/usr/lib/libstdc++.6.dylib: Mach-O universal binary with 3 architectures
/usr/lib/libstdc++.6.dylib (for architecture i386):     Mach-O dynamically linked shared library i386
/usr/lib/libstdc++.6.dylib (for architecture ppc7400):  Mach-O dynamically linked shared library ppc
/usr/lib/libstdc++.6.dylib (for architecture x86_64):   Mach-O 64-bit dynamically linked shared library x86_64

I would like for gcc to give me a /usr/local/lib/libstdc++.6.dylib for those same architectures, but my attempts to configure with --enable-multilib or --with-multilib-list=i386,ppc,x86_64 or --enable-targets=all were clearly misguided. Neither configure nor make generate errors, but all that gets generated is this:

[host:~] nsteiner% file /usr/local/lib/libstdc++.6.dylib
/usr/local/lib/libstdc++.6.dylib: Mach-O 64-bit dynamically linked shared library x86_64

Answer 1

Only Apple's GCC 4.2.1 still supports fat binaries. You'll have to take additional manual steps (or provide damn good wrapper scripts) to compile all sources twice, and run lipo on the resulting binaries.