package/libgeotiff: fix build without C++

package/libgeotiff: fix build without C++

Do not check for C++ compiler as libgeotiff is written in C otherwise
build will fail on toolchains without a working C++ compiler:

checking how to run the C++ preprocessor... /lib/cpp
configure: error: in
`/data/buildroot/buildroot-test/instance-1/output/build/libgeotiff-1.4.2':
configure: error: C++ preprocessor "/lib/cpp" fails sanity check

Fixes:
 - http://autobuild.buildroot.org/results/72f1c5c1b8fc337a1cff4b280abe99afd65f945b

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>