If mod_perl is to be installed (regardless of the SSL status), and if Perl, on the system, was installed with -lpthread, the following will have to be passed to the Apache configure script, that will be outlined in the next section:
# CFLAGS="-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64" \ LIBS="-lpthread" \ ./configure ........
One can always tell if they have a thread-enabled version of Perl by checking the version:
# perl -v This is perl, v5.8.3 built for i386-linux-thread-multi
Without the mention of threads, it is alright to proceed as normal without mentioning the LIBS line as above.