sizeof(int) in testsuite

[DJ Delorie]

gcc.dg/compat/struct-layout-1_generate.c assumes sizeof(int) is 4.
This of course fails on any target where sizeof(int) is 2.  They may
fail when sizeof(int) is 8 too, or at least they won't be testing the
full range of possibilities.

I've noticed that quite a few testcases make these types of
assumptions; they may or may not be xfailed for specific 16 bit
targets.

Do we have a standard way of telling the testsuite how big target
types are, or some standard "this test assumes 32 bit int" dejagnu
flag?