perl-5.12.1: Add -Dusethreads

Add -Dusethreads to make configuration similar to the configuration
of /usr/local/bin/perl.

perl-5.12.1-0.build.sh

@@ -85,7 +85,7 @@ sed -i -e '/"$cppstdin $Config/ s/cppstdin/cppstdin -P/' ext/Errno/Errno_pm.PL
 # -Duseshrplib : build shared perl library (required when perl is to be included in a shared library)
 # -DEBUGGING : add debugging code (perl -D)
 #
-./Configure -des -Duseshrplib -Dprefix=$PREFIX
+./Configure -des -Duseshrplib -Dusethreads -Dprefix=$PREFIX
 
 make -j$(nproc)