Merge #224: cmake: Improve Boost checks

e104fa9 fixup! cmake: Build `bitcoind` executable (Hennadii Stepanov)
b38d2bc fixup! cmake: Build `bitcoind` executable (Hennadii Stepanov)

Pull request description:

  The first commit was requested offline.

  The second commit speeds up configuration.

Top commit has no ACKs.

Tree-SHA512: c520fbe44c2601bc7052c411445f54a89a53352e71f67c1464bc96c413782f461449e95170cc519a9613942d78ee517de8d629c7c7e5f8b20226b7b37df0eff4

cmake/module/AddBoostIfNeeded.cmake

@@ -55,25 +55,14 @@ function(add_boost_if_needed)
   endif()
 
   if(BUILD_TESTS)
-    include(CheckCXXSourceCompiles)
-    check_cxx_source_compiles("
-      #define BOOST_TEST_MAIN
-      #include <boost/test/included/unit_test.hpp>
-      " HAVE_BOOST_INCLUDED_UNIT_TEST_H
-    )
+    # 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()
-
-    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()