MFC 308456: Pass the correct flag to find_symdef() from _rtld_bind().

MFC 308456: Pass the correct flag to find_symdef() from _rtld_bind().

When symbol versioning was added to rtld, the boolean 'in_plt' argument
to find_symdef() was converted to a bitmask of flags.  The first flag
added was 'SYMLOOK_IN_PLT' which replaced the 'in_plt' bool.  This
happened to still work by accident as SYMLOOK_IN_PLT had the value of 1
which is the same as 'true', so there should be no functional change.

git-svn-id: svn://svn.freebsd.org/base/stable/10@309371 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f