OS 10.5.7, Python 2.6.2 sources. 

When I execute:

/configure --enable-framework=/Library/Frameworks \
--enable-universalsdk=/ \
MACOSX_DEPLOYMENT_TARGET=10.5 \
--with-universal-archs=all \
--with-readline-dir=/usr/local

configure fails with the error
checking size of wchar_t... configure: error: cannot compute sizeof
(wchar_t)

However, if I replace all with 64-bit, it works fine. I note that this
issue was reported for OS X 10.4 and fixed. But this still happens

gcc information is

Using built-in specs.
Target: i686-apple-darwin9
Configured with: /var/tmp/gcc/gcc-5490~1/src/configure
--disable-checking -enable-werror --prefix=/usr --mandir=/share/man
--enable-languages=c,objc,c++,obj-c++
--program-transform-name=/^[cg][^.-]*$/s/$/-4.0/
--with-gxx-include-dir=/include/c++/4.0.0 --with-slibdir=/usr/lib
--build=i686-apple-darwin9 --with-arch=apple --with-tune=generic
--host=i686-apple-darwin9 --target=i686-apple-darwin9
Thread model: posix
gcc version 4.0.1 (Apple Inc. build 5490)

Works for me (2.6.2 tarball, 10.5.8 PPC, gcc build 5493).

Check configure.log and search for the failing "wchar_t" section.  Also, 
try stripping your $PATH down to bare essentials, removing /opt/local/bin 
(MacPorts), /sw/bin (Fink), /usr/local/bin, etc.; it's possible you're 
picking up an unexpected version of one of the build chain tools.

Thanks for the pointer. Indeed, clearing PATH to the minimal set of
paths allows configure to complete.