* defaults.h (EXTRA_MEMORY_CONSTRAINT): Provide a default.
(EXTRA_ADDRESS_CONSTRAINT): Likewise.
* doc/tm.texi: Document these two new target macros.
* config/s390/s390.c (s390_expand_plus_operand): Accept already
valid operands.
(q_constraint): New function.
config/s390/s390-protos.h (q_constraint): Declare it.
config/s390/s390.h (EXTRA_CONSTRAINT): Use it.
(EXTRA_MEMORY_CONSTRAINT): New macro.
* config/s390/s390.md: Throughout the machine description,
replace all instances of the constraint combinations 'Qo'
or 'oQ' with simply 'Q'.