I finally managed to compile the ARP shared library for the c6x architecture.

However, I have done it with a very dirty workaround.
First of all I call the configure with:

ac_cv_file__dev_zero=yes ac_cv_func_setpgrp_void=yes apr_cv_process_shared_works=yes apr_cv_mutex_robust_shared=yes apr_cv_tcp_nodelay_with_cork=yes ac_cv_sizeof_struct_iovec=8 apr_cv_mutex_recursive=yes ac_enable_shared=yes ac_enable_static=no ./configure --enable-static --host=c6x --prefix=$(pwd)/output CC=c6x-uclinux-gcc AR=c6x-uclinux-ar IDL_CPP=cpp ARFLAGS=rv --disable-ipv6 OBJDUMP=c6x-uclinux-objdump build_libtool_libs=yes AS=c6x-uclinux-as NM=c6x-uclinux-nm deplibs_check_method="pass_all" STRIP=c6x-uclinux-strip RANLIB=c6x-uclinux-ranlib CFLAGS=" -pipe -Os "

Once configuration is done I need to go into libtool file and edit the following:

(old  ---> new)

build_libtool_libs=no --- > build_libtool_libs=yes

deplibs_check_method="unknown" ---> deplibs_check_method="pass_all"

library_names_spec="" --- > library_names_spec="\${libname}\${release}\${shared_ext}\$versuffix \${libname}\${release}\${shared_ext}\$major \$libname\${shared_ext}"

then i run make && make install

And voila! :)

The problem here is that the host system (the c6x architecture) is not known to the configure script.
In libtool, the host system is specified as follows:

# The host system.
Maybe it's a good idea to add this to future builds?