sln: use stat64

When using sln on some filesystems which return 64-bit inodes,
the stat call might fail during install like so:
	.../elf/sln .../elf/symlink.list
	/lib32/libc.so.6: invalid destination: Value too large for defined data type
	/lib32/ld-linux.so.2: invalid destination: Value too large for defined data type
	Makefile:104: recipe for target 'install-symbolic-link' failed

Switch to using stat64 all the time to avoid this.

URL: https://bugs.gentoo.org/576396
(cherry picked from commit f5e753c8)