Looks like the 1.5.3 configure script inadvertently dropped support for alternate cURL library path support via --with-libcurl:
Yes, because it's the crappy way to do it. The right way is to export a variable to specify the PKG_CONFIG_PATH to the correct *.pc file. See my RPMs for reference...
Sorry for bringing this up again but how do i compile >=1.5.3 without installing curl?