pgsql: Fix included file path for modern perl

Fix included file path for modern perl

Contrary to the comment on 772d4b76, only paths starting with "./" or
"../" are considered relative to the current working directory by perl's
"do" function. So this patch converts all the relevant cases to use "./"
paths. This only affects MSVC.

Backpatch to all live branches.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/f83419b7396fe5c64613838fd9eab8424591ad4a

Modified Files
--------------
src/tools/msvc/Install.pm   | 4 ++--
src/tools/msvc/build.pl     | 6 +++---
src/tools/msvc/install.pl   | 2 +-
src/tools/msvc/mkvcbuild.pl | 4 ++--
src/tools/msvc/pgbison.pl   | 2 +-
src/tools/msvc/pgflex.pl    | 2 +-
src/tools/msvc/vcregress.pl | 6 +++---
7 files changed, 13 insertions(+), 13 deletions(-)