MIPS' sys/user.h currently has a constant definition for PAGE_SIZE, and 
the other related settings. This is not appropriate for XLP (and other 
MIPS?) where the actual page size is a kernel configuration option.

Apart from the general principle of not having incorrect definitions, 
the actual problem that needs to be solved is in 
sysdeps/unix/sysv/linux/ifaddrs.c in which PAGE_SIZE is used by 
preference as an optimization. Most of the other possible use cases 
prefer to call __getpagesize or use sysconf, and so are unaffected.

Clearly, keeping the constant definition is desirable on at least some 
MIPS variants, in order to keep the optimization, but not for XLP.

The attached patch makes the definition conditional, rather than 
removing it completely. It's not clear to me whether the HOST_* 
definitions are similarly affected, but other platforms that do not 
define PAGE_SIZE also choose not to define those, so I've extended the 
ifndef similarly.

I this OK to commit? Should it be solved a different way?

Testcase tst-limits does check PAGE_SIZE matches, if defined, but not in 
this case because that test case does not include sys/user.h. Should I 
create a new test case for this, or include that header in the existing 
test?

Thanks

Andrew