leptonica: fix static build issue

leptonica: fix static build issue

leptonica configure script does not use pkg-config to find the TIFF library,
so it doesn't know about the transitive dependencies of the TIFF library.
Switching to PKG_CHECK_MODULES() to discover the library solves the issue.

Fixes:
http://autobuild.buildroot.net/results/8dd2bcc41e861bdd324dd081e39925964d1ac428
http://autobuild.buildroot.net/results/ec7366d69b00625b652915fa58e3143f1bdcaf62
http://autobuild.buildroot.net/results/0cd74312a39e3bc59d15789a4c0a891f0f417b8c
http://autobuild.buildroot.net/results/35f9a0f2db30dd62733142f0fcfa72699452583f
http://autobuild.buildroot.net/results/f7ea889b2fb96ff7de492e282820c800187573cb

Signed-off-by: Gilles Talis <gilles.talis@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>