Merge bitcoin/bitcoin#33077: kernel: create monolithic kernel static library

fdbade6f8d kernel: create monolithic kernel static library (Cory Fields)

Pull request description:

  Currently, consuming `libbitcoinkernel.a` requires all its dependency static libraries to be available. A switch to a monolithic variant, which contains object files from its dependencies, was discussed in the Kernel WG. The necessary preparations in the libsecp256k1 build scripts were completed in https://github.com/bitcoin-core/secp256k1/pull/1678, which are now available in this repository since https://github.com/bitcoin/bitcoin/pull/33036.

  The changes in this PR were picked from https://github.com/theuni/bitcoin/commits/static_kernel/, with an additional adjustment in `libbitcoinkernel.pc.in`.

  This PR can be tested as described in https://github.com/bitcoin/bitcoin/pull/30814#issue-2505698234.

ACKs for top commit:
  TheCharlatan:
    ACK fdbade6f8d
  stickies-v:
    tACK fdbade6f8d

Tree-SHA512: bd9e9dbb0b765bdcb162fb3f4ad3c4e01fe5fa0b7061f97d0bad64442b21db036cbe0e4341fd45d43a8862df76d62c9532ca8945f76423aca753c6b528f70873

libbitcoinkernel.pc.in

@@ -7,5 +7,4 @@ Name: @CLIENT_NAME@ kernel library
 Description: Experimental library for the @CLIENT_NAME@ validation engine.
 Version: @CLIENT_VERSION_STRING@
 Libs: -L${libdir} -lbitcoinkernel
-Libs.private: -L${libdir} @LIBS_PRIVATE@
 Cflags: -I${includedir}

src/kernel/CMakeLists.txt

@@ -79,20 +79,23 @@ add_library(bitcoinkernel
   ../validation.cpp
   ../validationinterface.cpp
   ../versionbits.cpp
+  $<TARGET_OBJECTS:bitcoin_clientversion>
+  $<TARGET_OBJECTS:bitcoin_crypto>
+  $<TARGET_OBJECTS:leveldb>
+  $<TARGET_OBJECTS:crc32c>
 )
 target_link_libraries(bitcoinkernel
   PRIVATE
     core_interface
-    bitcoin_clientversion
-    bitcoin_crypto
-    leveldb
-    secp256k1
+    secp256k1_objs
     $<$<PLATFORM_ID:Windows>:bcrypt>
     $<TARGET_NAME_IF_EXISTS:USDT::headers>
   PUBLIC
     Boost::headers
 )
 
+target_include_directories(bitcoinkernel PRIVATE $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/src/leveldb/include>)
+
 # libbitcoinkernel requires default symbol visibility, explicitly
 # specify that here so that things still work even when user
 # configures with -DREDUCE_EXPORTS=ON
@@ -107,34 +110,6 @@ set_target_properties(bitcoinkernel PROPERTIES
 add_custom_target(libbitcoinkernel)
 add_dependencies(libbitcoinkernel bitcoinkernel)
 
-# When building the static library, install all static libraries the
-# bitcoinkernel depends on.
-if(NOT BUILD_SHARED_LIBS)
-  # Recursively get all the static libraries a target depends on and put them in libs_out
-  function(get_target_static_link_libs target libs_out)
-    get_target_property(linked_libraries ${target} LINK_LIBRARIES)
-    foreach(dep ${linked_libraries})
-      if(TARGET ${dep})
-        add_dependencies(libbitcoinkernel ${dep})
-        get_target_property(dep_type ${dep} TYPE)
-        if(dep_type STREQUAL "STATIC_LIBRARY")
-          list(APPEND ${libs_out} ${dep})
-          get_target_static_link_libs(${dep} ${libs_out})
-        endif()
-      endif()
-    endforeach()
-    set(${libs_out} ${${libs_out}} PARENT_SCOPE)
-  endfunction()
-
-  set(all_kernel_static_link_libs "")
-  get_target_static_link_libs(bitcoinkernel all_kernel_static_link_libs)
-
-  install(TARGETS ${all_kernel_static_link_libs} ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR} COMPONENT libbitcoinkernel)
-  list(TRANSFORM all_kernel_static_link_libs PREPEND "-l")
-  # LIBS_PRIVATE is substituted in the pkg-config file.
-  list(JOIN all_kernel_static_link_libs " " LIBS_PRIVATE)
-endif()
-
 configure_file(${PROJECT_SOURCE_DIR}/libbitcoinkernel.pc.in ${PROJECT_BINARY_DIR}/libbitcoinkernel.pc @ONLY)
 install(FILES ${PROJECT_BINARY_DIR}/libbitcoinkernel.pc DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig" COMPONENT libbitcoinkernel)