Add configure --disable-textrelcheck option to enable CC=afl-fuzz on 32bit.

Add configure --disable-textrelcheck option to enable CC=afl-fuzz on 32bit.

Using american fuzzy lop has found a lot of issues. It would be nice to
make using it a bit easier. Our build files make sure that no shared
library uses text relocations, but afl-gcc will insert some on i686.
http://www.akkadia.org/drepper/textrelocs.html

Now CC=afl-gcc ./configure --disable-textrelcheck will allow them so
that afl can instrument the libraries.

Don't try to use or install them except with afl-fuzz. When selinux is
enabled it might prevent loading the libraries with DT_TEXTREL set.

Signed-off-by: Mark Wielaard <mjw@redhat.com>