spandsp: fix static build with jpeg enabled

spandsp: fix static build with jpeg enabled

When jpeg is enabled libtiff links with it, but the spandsp configure
test doesn't take that into account, so the configure test fails. Use
pkg-config to add the required tiff dependencies.

Fixes:
http://autobuild.buildroot.net/results/243/243f1d1271a767556e0a4cd56a42fcc8c1a371ed/
http://autobuild.buildroot.net/results/485/48527e144bc4ad3eaab807f302888380bd9e78bb/
http://autobuild.buildroot.net/results/058/05885325ec274cb9860d423c57eed5e7063aedc0/

Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>