gtk: support libadwaita at least back to version 1.2 for Debian 12

[jcollie]

Discussed in #5787

^{Originally posted by kyleam February 15, 2025}
With the merge of 25c5ecf (gtk: require libadwaita, 2025-02-14) from gh-5749, building on Debian stable (12, bookworm) fails with

src/apprt/gtk/Window.zig:173:30: error: root struct of file 'cimport' has no member named 'adw_tab_button_new'
                const btn = c.adw_tab_button_new();
                            ~^~~~~~~~~~~~~~~~~~~

and

src/apprt/gtk/Window.zig:368:10: error: root struct of file 'cimport' has no member named 'adw_tab_overview_set_show_start_title_buttons'
        c.adw_tab_overview_set_show_start_title_buttons(

adw_tab_button_new and adw_tab_overview_set_show_start_title_buttons were not introduced until libadwaita 1.3.0.

Debian 12 has libadwaita 1.2.2.

$ apt-cache policy libadwaita-1-dev
libadwaita-1-dev:
  Installed: 1.2.2-1
  Candidate: 1.2.2-1
  Version table:
 *** 1.2.2-1 500
        500 http://deb.debian.org/debian bookworm/main amd64 Packages
        100 /var/lib/dpkg/status

It may be that the intent of gh-5749 was to drop support for libadwaita versions before 1.3.0, but, glancing through the PR, I don't see that explicitly state. @jcollie, can you confirm?

---

Related discussion (from prior to the merge of gh-5749): gh-5072

cc: @jneuhaus

[jcollie]

We didn't really have an "official" written policy as to what version of libadwaita that we supported but based on discussions on Discord we've decided to support at least 1.2 since that's what's in Debian stable. Once Debian 13 is released and is marked as stable that may change we'll revisit the policy. Of course, there may be advanced functionality that is not available if you compile with an older version but we want Ghostty to continue to work on Debian 12.