* config/s390/s390x.mt (GDB_MULTI_ARCH): Change to

GDB_MULTI_ARCH_PARTIAL.
* config/s390/s390.mt (GDB_MULTI_ARCH): Ditto.

* config/s390/tm-linux.h (SKIP_TRAMPOLINE_CODE): Undefine
definition from config/tm-linux.h.  Allow gdbarch to override it.
* config/tm-sysv4.h: Revert.  Handled by tm-linux.h.