[klibc] Fix size of size_t on parisc

[H. Peter Anvin]

Jeff Bailey wrote:
> On parisc-linux, gcc defines size_t as unsigned int:
> 
> # 1 "<built-in>"
> #define __SIZE_TYPE__ unsigned int
> 
> This mismatch causes dash to fail to build because of a malloc parameter
> mismatch.
> 

Hmmm... do we know how far back that gcc has had these defines?  In many 
ways the cleanest would be to simply use them.

	-hpa