Problem with std_expand_builtin_va_start on targets where sizetype and ptr_type_node don't have the same mode

[Paolo Bonzini]

> libstdc++'s bitmap_allocator.cc, because for some reason reload wants
> a MODE_PARTIAL_INT mode with 64 bits.  There is no such mode, so
> get_smallest_mode_for_size aborts.  I am attaching the .lreg and .greg
> dumps to this message (compressed).

Naively speaking, shouldn't it also look for MODE_INTs?  This might not 
be as easy as modifying genmodes if we want to do it in general, because 
for example we'd have PSI->SI->PDI->DI when iterating over 
MODE_PARTIAL_INT and SI->DI when iterating over MODE_INT.

Paolo