pgsql: Fix MSVC build script's check for obsolete node support function

Fix MSVC build script's check for obsolete node support functions.

Commit 964d01ae9 was a few bricks shy of a load here: the script
checked whether gen_node_support.pl itself had been updated since it
was last run, but not whether any of its input files had been updated.
Fix that. While here, scrape the list of input files from the
Makefiles rather than having a duplicate copy, as we do for most
other lists of source files.

In passing, improve gen_node_support.pl's error report for an
incorrect file list.

Per gripe from Amit Kapila.

Discussion: https://postgr.es/m/CAA4eK1KQk4vP-3mTAz26h-PRUZaGu8Fc=q-ZKSajsAthH0A15w@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/9a9f25e217428cdf4119ff08b77f9f5bd45f563c

Modified Files
--------------
src/backend/nodes/gen_node_support.pl | 2 +-
src/tools/msvc/Solution.pm | 50 +++++++++++++++--------------------
2 files changed, 23 insertions(+), 29 deletions(-)