configure: Promote SQLite3 "not installed" warning to error

Since Asterisk won't build without the library, not having it is definitely
an error. Thanks to Kyle Kurz for pointing this out.
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Merged revisions 432280 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 432281 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@432282 65c4cc65-6c06-0410-ace0-fbb531ad65f3