Use 'use strict' in all Perl programs

contrib/seg/seg-validate.pl

contrib/seg/sort-segments.pl

doc/src/sgml/mk_feature_tables.pl

src/pl/plperl/plc_perlboot.pl

src/test/locale/sort-test.pl

src/tools/msvc/build.pl

src/tools/msvc/gendef.pl

src/tools/msvc/pgflex.pl

src/tools/pginclude/pgcheckdefines

src/tools/version_stamp.pl