archr: symlink PortMaster compat libs into the default linker path

PortMaster runtimes failed to launch: love_11.5's love.aarch64 died with
"error while loading shared libraries: libtheoradec.so.1: cannot open
shared object file" (caught live over SSH while a port was launched).

Root cause: ArchR keeps the ~50 PortMaster compat libraries (older
Debian-11-era SONAMEs: libtheoradec.so.1, libavcodec.so.58,
libwebp.so.6, libx264.so.160, etc.) under /usr/lib/compat to stay out of
the base system, and the image ships NO ld.so.cache. glibc's dynamic
linker therefore only searches the hardcoded /usr/lib + /lib plus
LD_LIBRARY_PATH, so /usr/lib/compat is invisible to anything that does
not explicitly prepend it. control.txt does set
LD_LIBRARY_PATH=/usr/lib/compat, but the per-runtime invocation
overwrites it, dropping compat for binaries like love.aarch64.

docs/PortMaster_CFW.md is explicit on the fix: "add these older .so
symlinks alongside [the newer versions]" and "Keep [libtheoradec] at
standard versions." So we expose the compat SONAMEs in the default path.

New archr-compat-symlinks script + archr-compat-libs.service oneshot
(ordered Before=archr-autostart so it runs before any port launches):
walks /usr/lib/compat (and /usr/lib32/compat) and symlinks each SONAME
into /usr/lib, but ONLY when the base system does not already provide
that exact name, so real libraries (libogg.so.0, libvorbis.so.0, ...)
are never shadowed. Idempotent via the `[ -e ]` guard; the writable
ext4 rootfs keeps the links so later boots are no-ops.

Verified live on the R36S: 46 compat-only SONAMEs linked into /usr/lib,
libtheoradec.so.1 now resolvable, libogg.so.0 left untouched (still the
real /usr/lib/libogg.so.0.8.6).

projects/ArchR/packages/archr/package.mk

@@ -153,6 +153,12 @@ EOF
   ### Take a backup of the system configuration on shutdown
   enable_service save-sysconfig.service
 
+  ### Expose PortMaster compat libs (/usr/lib/compat) in the default
+  ### linker path. No ld.so.cache ships, so love_11.5 et al. fail on
+  ### libtheoradec.so.1 unless it is symlinked into /usr/lib (see
+  ### docs/PortMaster_CFW.md and the archr-compat-symlinks script).
+  enable_service archr-compat-libs.service
+
   ### System locale. glibc/package.mk only generates en_US.UTF-8; without
   ### this file LANG stays empty and every shell falls back to POSIX,
   ### which breaks UTF-8 input, pacman messages and emulator menus.

projects/ArchR/packages/archr/sources/scripts/archr-compat-symlinks

@@ -0,0 +1,45 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# archr-compat-symlinks: expose the PortMaster compat libraries
+# (/usr/lib/compat/*.so*, the older Debian-11-era SONAMEs that ports and
+# their runtimes link against) in the default linker search path.
+#
+# ArchR keeps these libs under /usr/lib/compat to stay out of the base
+# system, but the image ships no ld.so.cache: the dynamic linker only
+# searches the hardcoded /usr/lib + /lib plus LD_LIBRARY_PATH, so
+# /usr/lib/compat is invisible to anything that does not explicitly
+# prepend it. PortMaster runtimes such as love_11.5 link
+# libtheoradec.so.1 as a normal system library and die with
+# "cannot open shared object file: libtheoradec.so.1" when it lives only
+# under compat. docs/PortMaster_CFW.md is explicit: "add these older .so
+# symlinks alongside [the newer versions]" and "Keep [libtheoradec] at
+# standard versions."
+#
+# We therefore symlink each compat lib into /usr/lib, but ONLY when the
+# base system does not already provide that exact SONAME, so we never
+# shadow a real system library (e.g. libogg.so.0, libvorbis.so.0).
+#
+# Idempotent: the `[ -e ]` guard skips anything already present, so it is
+# safe to run every boot. The rootfs is writable ext4, so the links
+# persist and later boots are no-ops.
+
+link_dir() {
+  local compat="$1" libdir="$2" n=0 f base
+  [ -d "${compat}" ] || return 0
+  for f in "${compat}"/*.so*; do
+    [ -e "${f}" ] || continue
+    base="${f##*/}"
+    if [ ! -e "${libdir}/${base}" ]; then
+      ln -sf "compat/${base}" "${libdir}/${base}" && n=$((n + 1))
+    fi
+  done
+  echo "${n}"
+}
+
+created=$(link_dir /usr/lib/compat /usr/lib)
+# armhf / 32-bit ports use the lib32 tree when present.
+created32=$(link_dir /usr/lib32/compat /usr/lib32)
+
+echo "archr-compat-symlinks: linked ${created:-0} (lib) + ${created32:-0} (lib32) compat SONAMEs into the default path"
+exit 0

projects/ArchR/packages/archr/system.d/archr-compat-libs.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=ArchR PortMaster compat library symlinks
+# Ports are launched from EmulationStation, which archr-autostart.service
+# brings up; ordering before it guarantees the compat SONAMEs are linked
+# into /usr/lib before any port (or its runtime) can dlopen them.
+Before=archr-autostart.service
+After=systemd-tmpfiles-setup.service
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/archr-compat-symlinks
+RemainAfterExit=yes
+
+[Install]
+WantedBy=archr.target