fixup! cmake: Build bitcoind executable

Switch to `check_include_file_cxx` when checking headers.
This speeds up configuration.

Only one Boost.Test header is being checked now.

cmake/module/AddBoostIfNeeded.cmake

@@ -57,25 +57,12 @@ function(add_boost_if_needed)
   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.
-    include(CheckCXXSourceCompiles)
-    check_cxx_source_compiles("
-      #define BOOST_TEST_MAIN
-      #include <boost/test/included/unit_test.hpp>
-      " HAVE_BOOST_INCLUDED_UNIT_TEST_H
-    )
+    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()
-
-    check_cxx_source_compiles("
-      #define BOOST_TEST_MAIN
-      #include <boost/test/included/unit_test.hpp>
-      #include <boost/test/unit_test.hpp>
-      " HAVE_BOOST_UNIT_TEST_H
-    )
-    if(NOT HAVE_BOOST_UNIT_TEST_H)
-      message(FATAL_ERROR "Building test_bitcoin executable requested but boost/test/unit_test.hpp header not available.")
-    endif()
   endif()
 
 endfunction()