cmake: Build test_bitcoin executable

cmake/module/AddBoostIfNeeded.cmake

@@ -64,4 +64,15 @@ function(add_boost_if_needed)
     set(CMAKE_REQUIRED_DEFINITIONS)
   endif()
 
+  if(BUILD_TESTS)
+    # Some package managers, such as vcpkg, vendor Boost.Test separately
+    # from the rest of the headers, so we have to check for it individually.
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS -DBOOST_TEST_NO_MAIN)
+    include(CheckIncludeFileCXX)
+    check_include_file_cxx(boost/test/included/unit_test.hpp HAVE_BOOST_INCLUDED_UNIT_TEST_H)
+    if(NOT HAVE_BOOST_INCLUDED_UNIT_TEST_H)
+      message(FATAL_ERROR "Building test_bitcoin executable requested but boost/test/included/unit_test.hpp header not available.")
+    endif()
+  endif()
+
 endfunction()