distcc-avahi: 3.4-18 — fix DISTCC_ARGS/DISTCC_OPTS drift on upgrade (closes #5)

Stock distcc and earlier distcc-avahi releases ship /etc/conf.d/distccd
with DISTCC_ARGS=, while our distccd.service reads $DISTCC_OPTS. On
hosts that had stock distcc installed first, pacman keeps the existing
conf file (it's marked backup=) so the rename never happens — distccd
starts with empty options, falls back to --allow-private, and warns
about missing /usr/lib/distcc masquerade dir.

Add a post_install/post_upgrade .install hook that:
- detects DISTCC_ARGS= in /etc/conf.d/distccd and renames to DISTCC_OPTS=
  (keeping a timestamped backup beside it)
- runs update-distcc-symlinks if /usr/lib/distcc is unpopulated
- prompts the operator to restart distccd if it's already active

Bumps pkgrel to 18.

Hit on ampere 2026-04-29 during fourier-campaign distcc enrollment;
likely lurking on every host with stock-distcc legacy state.

arch/distcc-avahi/PKGBUILD

@@ -10,7 +10,7 @@
 pkgname=distcc-avahi
 _pkgname=distcc
 pkgver=3.4
-pkgrel=17
+pkgrel=18
 pkgdesc="Distributed compilation service for C, C++ and Objective-C (with Avahi/Zeroconf support)"
 arch=('x86_64' 'aarch64')
 url="https://github.com/distcc/distcc"
@@ -22,12 +22,14 @@ provides=("distcc=${pkgver}")
 conflicts=('distcc')
 replaces=('distcc')
 backup=('etc/conf.d/distccd')
+install=${pkgname}.install
 source=(
     "${_pkgname}-${pkgver}.tar.gz::https://github.com/distcc/distcc/archive/refs/tags/v${pkgver}.tar.gz"
     "distccd.conf"
     "distccd.service"
     "distcc.tmpfiles"
     "fix-gcc-rewrite-fqn-overflow.patch"
+    "${pkgname}.install"
 )
 sha256sums=(
     '37a34c9555498a1168fea026b292ab07e7bb394715d87d8403e0c33b16d2d008'
@@ -35,6 +37,7 @@ sha256sums=(
     'a4f1d1bb21d61d41f22e918b448cfb852a6d95b0d3b922bd82805090cb2ce41a'
     'd8aee2eb895c02a39e0f2b76fd4a5c9dce91405f1c443286ca324628eadbf3f1'
     '7ff56af2ea505bfbf65ceeb0c8f752295f73ffb1173c26a6e978840fad04f651'
+    'f7d5e02298db44f46763b28ca509e9151e8331ce8cc9a732f1b5f49923d03f47'
 )
 
 prepare() {