Makefile: add installcheck-existing target and improve readability

[jrgemignani]

Add an "installcheck-existing" target that runs the regression suite against an already-running PostgreSQL server, complementing the default "installcheck" (which builds a private temp instance). It points pg_regress at the server via the standard libpq variables (PGHOST/PGPORT/PGUSER; PGDATABASE defaults to contrib_regression) and lets pg_regress create the database and load the extension through --load-extension=age. It deliberately avoids --use-existing -- that option skips database creation and disables --load-extension -- so no manual CREATE EXTENSION step is required. The upgrade test (age_upgrade) is excluded because it stages synthetic extension files into the local sharedir that a running server would not see.

Readability and maintainability improvements (no behavior change):

• Derive age_sql from AGE_CURR_VER (read from age.control) so the version number is defined in exactly one place.
• Add section banners and a top-of-file layout/target index; group the scattered upgrade-test pieces and move the ag_scanner flex rule in with the other parser-generation rules.
• Wrap the long REGRESS_OPTS and EXTRA_CLEAN assignments across lines.
• Fix the DATA filter-out pattern to use a double dash (age--%--y.y.y.sql) matching the actual template filename; the prior single-dash pattern only matched via greedy '%' expansion.
• Anchor the age.control version regex (/^default_version/).
• Replace the hardcoded "31 tests" comment with generic wording and add a "help" target listing the common targets.

Verified on PostgreSQL 18: make installcheck (temp instance) and make installcheck-existing both pass; clean rebuild and make clean unaffected.

Co-authored-by: GitHub Copilot noreply@github.com

modified: Makefile

[Copilot]

Pull request overview

This PR extends the extension build/test Makefile by adding an installcheck-existing target to run the regression suite against an already-running PostgreSQL server (via libpq connection parameters), while also restructuring the Makefile for improved readability and reduced duplication (e.g., deriving the install SQL filename from age.control).

Changes:

• Add installcheck-existing to run pg_regress against a running server and exclude the synthetic upgrade regression test from that path.
• Derive age_sql from AGE_CURR_VER (read from age.control) and tighten/clarify upgrade-test related patterns and regexes.
• Reorganize/annotate Makefile sections and wrap long variable assignments for maintainability.

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