build: speedup by simplifying dependency graph

Allow the objects of static libs to be built in parallel rather than serially
based on their dependency ordering.

For more detail, see:
https://cmake.org/cmake/help/latest/prop_tgt/OPTIMIZE_DEPENDENCIES.html

CMakeLists.txt

@@ -40,6 +40,11 @@ set(CMAKE_TRY_COMPILE_PLATFORM_VARIABLES
   CMAKE_CXX_LINK_EXECUTABLE
 )
 
+# Flatten static lib dependencies.
+# Without this, if libfoo.a depends on libbar.a, libfoo's objects can't begin
+# to be compiled until libbar.a has been created.
+set(CMAKE_OPTIMIZE_DEPENDENCIES TRUE)
+
 project(BitcoinCore
   VERSION ${CLIENT_VERSION_MAJOR}.${CLIENT_VERSION_MINOR}.${CLIENT_VERSION_BUILD}
   DESCRIPTION "Bitcoin client software"

src/util/CMakeLists.txt

@@ -36,6 +36,9 @@ add_library(bitcoin_util STATIC EXCLUDE_FROM_ALL
   ../sync.cpp
 )
 
+# Workaround for https://gitlab.kitware.com/cmake/cmake/-/issues/24058
+set_target_properties(bitcoin_util PROPERTIES OPTIMIZE_DEPENDENCIES OFF)
+
 target_link_libraries(bitcoin_util
   PRIVATE
     core_interface