Add Metamod-R timer fallback and static libstdc++ for legacy gamemod ABI

[APGRoboCop]

Summary

• adminmod_timer fallback for Metamod-R. CREATE_NAMED_ENTITY("adminmod_timer") returns null on Metamod-R because it doesn't expose LINK_ENTITY_TO_PLUGIN; previously this aborted the DLL via am_exit(1) and silently broke every timer-driven say command (timeleft, nextmap, votes). On null we now spin up a free-standing CTimer backed by a static entvars_t and poll its nextthink from AM_StartFrame() instead of relying on the engine to fire it. GetAdminTimer() centralises the lookup so callers don't care which path is active.
• Static libstdc++/libgcc on Linux. The previous Makefile had -static-libstdc++ on the compile line (no-op with -c) and -nodefaultlibs on the link line (which stripped libstdc++ before anything could re-add it), so the resulting .so dynamically depended on the build host's libstdc++.so.6. That broke loading on pre-SteamPipe gamemod hosts (TS3 3.0, Action Half-Life, FireArms 3.0). Moved the static flags to SHLIBLDFLAGS where they actually take effect, dropped -nodefaultlibs, added -Wl,--no-as-needed, and cleared the malformed STDCPPLIB=-L<path-to-.so> (-L takes a directory).
• Migrated remaining GET_PRIVATE(pTimerEnt) call sites in admin_commands.cpp (changelevel, kill_timer, get_timer, set_timer, vote_multiple, vote_allowed) to GetAdminTimer() so they work in fallback mode. vote_allowed would otherwise have silently returned 0 forever under Metamod-R.

Why

Reported by a server admin running Metamod-R: AdminMod refuses to load. Independently, the SteamPipe-built Linux .so doesn't load against legacy gamemods (TS3/AHL/FA3), forcing them to stay on AdminMod 2.50.60. Both root causes are addressed here -- the fallback restores Metamod-R support without affecting Metamod-P/-AM (which keep the original entity path), and the static-runtime build matches what AMXX 1.8.2+ does on Linux for cross-host compatibility.

Test plan

• Build Ometamod target on Linux. Confirm ldd admin_mm_i386.so shows no libstdc++.so.6 or libgcc_s.so.1 dependency.
• Run on a stock HLDS + Metamod-P server: confirm no warning, say timeleft/say nextmap/vote_multiple work as before.
• Run on a Metamod-R server: confirm console shows WARNING: CREATE_NAMED_ENTITY failed for adminmod_timer; using AM_StartFrame polling fallback, then timer-driven say commands fire correctly.
• Run on legacy (pre-SteamPipe) gamemod hosts: TS3 3.0, Action Half-Life, FireArms 3.0.
• Map change with changelevel intermission timer set: confirm the timer survives and fires on the next map.

Reviewer notes

• The Windows path is unchanged. admin_mod_mm.dll users won't see any behavior change.
• s_fallbackTimer is a single static instance with module lifetime; AM_Initialize() resets s_bTimerFallbackActive so each map change re-detects whether the entity link is available.
• The static-libstdc++ approach means C++ exceptions can't propagate across the AdminMod <-> gamemod boundary. AdminMod doesn't currently throw across that boundary, so this is fine, but worth flagging for future code.

🤖 Generated with Claude Code