try to force 32-bit package for centos7 i386

packaging/rpm.cmake

@@ -16,6 +16,9 @@ set(CPACK_RPM_PACKAGE_REQUIRES "systemd, iproute, libstdc++")
 set(CPACK_RPM_PACKAGE_REQUIRES_PRE "/usr/sbin/useradd, /usr/bin/getent")
 set(CPACK_RPM_PACKAGE_OBSOLETES "zerotier-one")
 set(CPACK_PACKAGE_RELOCATABLE FALSE)
+if(BUILD_32BIT)
+    set(CPACK_RPM_PACKAGE_ARCHITECTURE "i386")
+endif()
 
 set(CPACK_RPM_PRE_INSTALL_SCRIPT_FILE "${CMAKE_CURRENT_SOURCE_DIR}/packaging/rpm/rpm.pre")
 set(CPACK_RPM_POST_INSTALL_SCRIPT_FILE "${CMAKE_CURRENT_SOURCE_DIR}/packaging/rpm/rpm.post")