pgsql: More fixed for modern perl on back branches

More fixed for modern perl on back branches

Use "do" instead of "require" for included files, as it doesn't look for
them in the search path but relative to the current working directory.
These changes have already been made to REL_10_STABLE and later, to
satisfy the demands of perlcritic, but need backporting now to earlier
branches.

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/772d4b769d30090dbf4434d7d192569b11371a53

Modified Files
--------------
src/tools/msvc/Install.pm | 4 ++--
src/tools/msvc/build.pl | 8 ++++----
src/tools/msvc/builddoc.pl | 2 +-
src/tools/msvc/install.pl | 4 ++--
src/tools/msvc/mkvcbuild.pl | 4 ++--
src/tools/msvc/pgbison.pl | 2 +-
src/tools/msvc/pgflex.pl | 2 +-
src/tools/msvc/vcregress.pl | 6 +++---
8 files changed, 16 insertions(+), 16 deletions(-)