[fix builds on arm] [fix boost builds]

cmake/libraries/boost.cmake

@@ -96,8 +96,10 @@ if(PROJECT_ENABLE_BOOST)
 
       if(PROJECT_ENABLE_LIBBITCOIN_SYSTEM)
         set(BOOST_CXX_STANDARD 14)
+        set(BOOST_OPTIONS cxxflags=-Wno-enum-constexpr-conversion)
       else()
         set(BOOST_CXX_STANDARD ${CMAKE_CXX_STANDARD})
+        set(BOOST_OPTIONS define=BOOST_ASIO_HAS_STD_STRING_VIEW)
       endif()
 
       set(BOOST_BUILD_ARGS
@@ -107,12 +109,11 @@ if(PROJECT_ENABLE_BOOST)
         architecture=${BOOST_ARCH}
         cxxstd-dialect=gnu
         cxxstd=${BOOST_CXX_STANDARD}
-        cxxflags=-Wno-enum-constexpr-conversion
-        define=BOOST_ASIO_HAS_STD_STRING_VIEW
         define=BOOST_SYSTEM_NO_DEPRECATED
         link=${BOOST_LINK}
         threading=multi
         variant=${BOOST_BUILD_TYPE_LOWER}
+        ${BOOST_OPTIONS}
       )
 
       ExternalProject_Add(boost_project