Per newer versions of glibc:

error: In the GNU C Library, "major" is defined
by <sys/sysmacros.h>. For historical compatibility, it is
currently defined by <sys/types.h> as well, but we plan to
remove this soon. To use "major", include <sys/sysmacros.h>
directly. If you did not intend to use a system-defined macro
"major", you should undefine it after including <sys/types.h>. [-Werror]
string path = str::stream() << "/sys/dev/block/" << major(dev) << ':' << minor(dev)

Including <sys/sysmacros.h> appears to be the correct solution to quiet the warning