Solved linking issue with pcl

[marbosjo]

This PR solves a linking problem with pcl::search::Search::getName method:

(.data.rel.ro._ZTVN3pcl6search6SearchINS_8PointXYZEEE[_ZTVN3pcl6search6SearchINS_8PointXYZEEE]+0x20): undefined reference to `pcl::search::Search<pcl::PointXYZ>::getName[abi:cxx11]() const'
CMakeFiles/align.dir/apps/align.cpp.o:(.data.rel.ro._ZTVN3pcl6search6KdTreeINS_8PointXYZENS_11KdTreeFLANNIS2_N5flann9L2_SimpleIfEEEEEE[_ZTVN3pcl6search6KdTreeINS_8PointXYZENS_11KdTreeFLANNIS2_N5flann9L2_SimpleIfEEEEEE]+0x20): undefined reference to `pcl::search::Search<pcl::PointXYZ>::getName[abi:cxx11]() const'
/home/mbosch/workspaces/ndt_omp/devel/.private/ndt_omp/lib/libndt_omp.so: undefined reference to `pcl::search::Search<pcl::PointXYZI>::getName[abi:cxx11]() const'
collect2: error: ld returned 1 exit status
make[2]: *** [/home/mbosch/workspaces/ndt_omp/devel/.private/ndt_omp/lib/ndt_omp/align] Error 1
make[1]: *** [CMakeFiles/align.dir/all] Error 2
make: *** [all] Error 2

Current setup:
ROS Kinetic (updated at 2019-08-19)
Ubuntu 16.04 (updated at 2019-08-19)
PCL 1.7 (libpcl1.7, 1.7.2-14build1)

Solution proposed comes from:
PointCloudLibrary/pcl#2406 (comment)

[koide3]

Thanks!