lib/libc/ssp/h_stpncpy.c breaks multiple builds

[Paul Goyette <paul%whooppee.com@localhost>]

With up-to-date sources, I'm seeing the following error on multiple 
ports (including evbcf, evbppc, mac68k, sun2, vax)

cc1: warnings being treated as errors
/build/netbsd-local/src/tests/lib/libc/ssp/h_stpncpy.c: In function 'main':
/build/netbsd-local/src/tests/lib/libc/ssp/h_stpncpy.c:44: warning: 
pointer/integer type mismatch in conditional expression

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