realpath: prefer the buffer size given by pathconf()
realpath: prefer the buffer size given by pathconf()

If realpath(..., NULL) doesn't work, we have to allocate a buffer
blindly.  Use the value returned from pathconf() in preference from
compile-time constants.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm