/usr/libexec/gcc/powerpc-apple-darwin10/4.2.1/as: assembler (/usr/bin/../libexec/gcc/darwin/ppc/as or /usr/bin/../local/libexec/gcc/darwin/ppc/as) for architecture ppc not installed... then I have a simple workaround for you. (If anyone has the proper way to reconfigure the build environment such that configure/autoconf properly detect the architectures without this hack, post it in the comments)
Installed assemblers are:
/usr/bin/../libexec/gcc/darwin/x86_64/as for architecture x86_64
/usr/bin/../libexec/gcc/darwin/i386/as for architecture i386
Either set permanently, temporarily, or within the execution context of your program, the ARCHFLAGS environment variable to x86_64, as I did here:
env ARCHFLAGS="-arch i386 -arch x86_64" cpan
Given that recent operating systems have dropped support for Rosetta, and that running under emulation would be slower than native, there's no point in building universal binaries on an Intel Mac anyway, so why this configuration is supported is beyond me.