32-bit build failure

[Andrew Stubbs]

Hi Martin,

It looks like your change r242000 broke builds on 32-bit hosts:

fold-const-call.c:1541:36: error: cannot convert 'size_t* {aka unsigned 
int*}' to 'long long unsigned int*' for argument '2' to 'const char* 
c_getstr(tree, long long unsigned int*)'

Basically, the code only works where HOST_WIDE_INT == size_t.

Andrew