libc/glibc: LinuxThreads are no longer supported in latest versions

In fact, it is only supported in a few legacy versions.

Keep LT available for all eglibc versions, although it might need
a similar safeguard...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # m68k specific configuration file

 # depends on EXPERIMENTAL

 config ARCH_m68k

     select ARCH_SUPPORTS_32

     select ARCH_DEFAULT_32

     select ARCH_DEFAULT_BE

     select ARCH_SUPPORT_CPU

      help

       The m68k architecture