multiprocess: Add bitcoin wrapper executable

Intended to make bitcoin command line features more discoverable and allow
installing new multiprocess binaries in libexec/ instead of bin/ so they don't
cause confusion.

Idea and implementation of this were discussed in
https://github.com/bitcoin/bitcoin/issues/30983

Co-authored-by: Sjors Provoost <sjors@sprovoost.nl>

CMakeLists.txt

@@ -94,6 +94,7 @@ endif()
 #=============================
 include(CMakeDependentOption)
 # When adding a new option, end the <help_text> with a full stop for consistency.
+option(BUILD_BITCOIN_BIN "Build bitcoin executable." ON)
 option(BUILD_DAEMON "Build bitcoind executable." ON)
 option(BUILD_GUI "Build bitcoin-qt executable." OFF)
 option(BUILD_CLI "Build bitcoin-cli executable." ON)
@@ -202,6 +203,7 @@ target_link_libraries(core_interface INTERFACE
 
 if(BUILD_FOR_FUZZING)
   message(WARNING "BUILD_FOR_FUZZING=ON will disable all other targets and force BUILD_FUZZ_BINARY=ON.")
+  set(BUILD_BITCOIN_BIN OFF)
   set(BUILD_DAEMON OFF)
   set(BUILD_CLI OFF)
   set(BUILD_TX OFF)
@@ -643,6 +645,7 @@ message("\n")
 message("Configure summary")
 message("=================")
 message("Executables:")
+message("  bitcoin ............................. ${BUILD_BITCOIN_BIN}")
 message("  bitcoind ............................ ${BUILD_DAEMON}")
 if(BUILD_DAEMON AND ENABLE_IPC)
   set(bitcoin_daemon_status ON)