liblzma: Silence a warning from MSVC.

It gives C4146 here since unary minus with unsigned integer
is still unsigned (which is the intention here). Doing it
with substraction makes it clearer and avoids the warning.

Thanks to Nathan Moinvaziri for reporting this.

src/liblzma/check/crc64_fast.c

@@ -256,7 +256,7 @@ crc64_clmul(const uint8_t *buf, size_t size, uint64_t crc)
 	// C = buf + size == aligned_buf + size2
 	// D = buf + size + skip_end == aligned_buf + size2 + skip_end
 	const size_t skip_start = (size_t)((uintptr_t)buf & 15);
-	const size_t skip_end = (size_t)(-(uintptr_t)(buf + size) & 15);
+	const size_t skip_end = (size_t)((0U - (uintptr_t)(buf + size)) & 15);
 	const __m128i *aligned_buf = (const __m128i *)(
 			(uintptr_t)buf & ~(uintptr_t)15);