Fix PowerPC segfault.

The segfault fix was originally developed by our upstream, sqlite.org,
to address S/390 and Sparc segfaults, both of which are big endian.
Our PowerPC is also big endian, which this patch also fixes.

Reported by: Mark Millard <marklmi at yahoo.com>
Tested by: Mark Millard <marklmi at yahoo.com>
Obtained from: https://www.sqlite.org/src/vinfo/04885763c4cd00cb?diff=1

		https://sqlite.org/forum/forumpost/672291a5b2

MFC after: 1 month
X-MFC with: r360221, 360221