dgb(#82): define dgb/dgb_coin libs unconditionally so coin-matrix links c2pool-dgb

The run-loop slice switched c2pool-dgb to link the dgb and dgb_coin OBJECT
libs, but both were defined only inside if(COIN_DGB). The coin-matrix CI job
configures without -DCOIN_DGB, so the targets were undefined and CMake emitted
raw -ldgb/-ldgb_coin, failing the link (cannot find -ldgb). Mirror btc/ltc,
which define their per-coin libs unconditionally; keep only the test subtree
behind COIN_DGB (build.yml sets the flag and builds those targets).

Verified: fresh configure with COIN_DGB=OFF builds + links c2pool-dgb and
--help smokes clean (EXIT=0).

Author: frstrtr

src/impl/dgb/CMakeLists.txt

@@ -1,5 +1,4 @@
-# c2pool-dgb coin module (V36). Built when -DCOIN_DGB=ON.
-# Mirrors src/impl/btc/CMakeLists.txt; emits the c2pool-dgb binary.
+# c2pool-dgb coin module (V36). Mirrors src/impl/btc/CMakeLists.txt.
 # Per-coin binary scheme: project_v36_per_coin_binary_v37_unified_process.
 # Impl plan: c2pool-dgb-embedded-impl-plan.md (frstrtr/the docs/v36, 8ef8d2d).
 #
@@ -11,30 +10,32 @@
 # in this module yet: parked behind the Phase 5.8 settle (ltc-doge owns the
 # shared DOGE-aux surface). Do not add AUX_DOGE plumbing here at M2.
 #
-# TODO(M3): add_library(impl_dgb ...) sources as an OBJECT lib (ci-steward
-# PR-CMake-object-library convention; impl_dgb = 1 of 5 per-coin OBJECT libs),
-# link bitcoin_family/Scrypt shared base, wire embedded DigiByte Core daemon
-# slice under daemon/. Top-level add_subdirectory(src/impl/dgb) registration
-# follows the OBJECT-lib convention PR; held ~2-3 heartbeats, not raced here.
+# LIB GATING (mirrors btc/ltc): the dgb_coin (coin-layer) and dgb (pool-layer)
+# OBJECT libs are defined UNCONDITIONALLY — the c2pool-dgb executable links
+# them, and the coin-matrix CI builds that exe WITHOUT -DCOIN_DGB, so the
+# targets MUST exist regardless of the flag (gating them behind COIN_DGB makes
+# the linker fall back to raw -ldgb/-ldgb_coin and fail). Only the test subtree
+# stays behind COIN_DGB; build.yml sets -DCOIN_DGB=ON and builds those targets.
+add_subdirectory(coin)
+# add_subdirectory(daemon)
+
+# dgb -- DGB Scrypt pool-layer OBJECT lib. Mirrors the ltc/btc OBJECT lib:
+# compiles the real NodeImpl translation unit (node.cpp + protocol handlers)
+# so share_tracker.hpp / share_check.hpp are pulled into a compiled TU. Links
+# the shared core / pool / sharechain base plus dgb_coin (embedded P2P+mempool)
+# and c2pool_storage (LevelDB sharechain).
+add_library(dgb OBJECT
+    config_coin.hpp config_coin.cpp config_pool.hpp config_pool.cpp
+    node.hpp node.cpp
+    peer.hpp
+    protocol_actual.cpp protocol_legacy.cpp
+    messages.hpp
+    share_types.hpp share.hpp
+)
+target_link_libraries(dgb core pool sharechain dgb_coin btclibs c2pool_storage ${SECP256K1_LIBRARIES})
+
 if(COIN_DGB)
   message(STATUS "c2pool: DGB Scrypt-only coin module enabled")
-  add_subdirectory(coin)
   add_subdirectory(stratum)   # dgb_stratum: IWorkSource (#82 miner-facing path)
-  # add_subdirectory(daemon)
   add_subdirectory(test)
-
-  # dgb -- DGB Scrypt pool-layer OBJECT lib. Mirrors the ltc OBJECT lib
-  # (src/impl/ltc/CMakeLists.txt): compiles the real NodeImpl translation unit
-  # (node.cpp + protocol handlers) so share_tracker.hpp / share_check.hpp are
-  # pulled into a compiled TU. Links the shared core / pool / sharechain base
-  # plus dgb_coin (embedded P2P+mempool) and c2pool_storage (LevelDB sharechain).
-  add_library(dgb OBJECT
-      config_coin.hpp config_coin.cpp config_pool.hpp config_pool.cpp
-      node.hpp node.cpp
-      peer.hpp
-      protocol_actual.cpp protocol_legacy.cpp
-      messages.hpp
-      share_types.hpp share.hpp
-  )
-  target_link_libraries(dgb core pool sharechain dgb_coin btclibs c2pool_storage ${SECP256K1_LIBRARIES})
 endif()