zend_register_functions () traverses a list, implemented as a 0-terminated
array, to register functions.  When passed the ext/xslt/sablot.c`xslt_functions[]
array, it crashes because there is no trailing entry whose p->fname member
is null.  Easy fix:
         PHP_FE(xslt_free, NULL)
 +      {0, 0, 0},
   };

./configure \
        --disable-force-cgi-redirect \
        --disable-short-tags \
        --enable-debugger \
        --enable-discard-path \
        --enable-maintainer-mode \
        --enable-mbstr-enc-trans \
        --enable-mbstring \
        --enable-safe-mode \
        --enable-track-dirs \
        --enable-track-vars \
        --enable-url-includes \
        --enable-wddx \
        --enable-xslt \
        --prefix=/usr/localhost \
        --with-apxs=/c0/http/apache_1.3.22/apache/sbin/apxs \
        --with-config-file-path=$PWD \
        --with-curl=/usr/localhost/new \
        --with-exec-dir=$PWD \
        --with-expat-dir=/usr/localhost \
        --with-iconv \
        --with-mysql=/c0/src/mysql/mysql-3.22.32-sun-solaris2.7-sparc \
        --with-pgsql=/opt/pgsql \
        --with-xslt-sablot \
        "$@" \
        < /dev/null

I also had to hack up the configure script to locate my sablot installation.
But that's another tale of woe.

Happy US national holiday!
S.