tesseract: cmake build fails on Ubuntu bionic because of old cmake version

cmake version 3.10.2 aborts the build:

CMake Error at src/training/CMakeLists.txt:4 (cmake_policy):
  Policy "CMP0074" is not known to this version of CMake.

Can this policy be set conditionally only for newer versions of cmake?

After removing the policy line, the build sets wrong linker options for Curl (caused by commit c4ad9b7bbf1a390872402cf52cc52e9e9f4901e2):

CMake Error at CMakeLists.txt:812 (add_executable):
  Target "tesseract" links to target "CURL::libcurl" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?
[...]

After fixing that locally, building tesseract works, but the training tools give linker errors:

[ 90%] Linking CXX executable ../../bin/text2image
cd /home/ubuntu/src/github/tesseract-ocr/tesseract/build/src/training && /usr/bin/cmake -E cmake_link_script CMakeFiles/text2image.dir/link.txt --verbose=1
/usr/bin/clang++-10  -O3 -DNDEBUG -Wno-unused-command-line-argument   CMakeFiles/text2image.dir/text2image.cpp.o CMakeFiles/text2image.dir/degradeimage.cpp.o  -o ../../bin/text2image libpango_training.a libunicharset_training.a libcommon_training.a ../../libtesseract.a -lpthread /usr/lib/powerpc64le-linux-gnu/libarchive.so /usr/lib/powerpc64le-linux-gnu/libcurl.so -llept 
/usr/bin/ld: libpango_training.a(ligature_table.cpp.o): undefined reference to symbol '_ZN6icu_608ByteSink5FlushEv'
//usr/lib/powerpc64le-linux-gnu/libicuuc.so.60: error adding symbols: DSO missing from command line
clang: error: linker command failed with exit code 1 (use -v to see invocation)
src/training/CMakeFiles/text2image.dir/build.make:126: recipe for target 'bin/text2image' failed
make[2]: *** [bin/text2image] Error 1
make[2]: Leaving directory '/home/ubuntu/src/github/tesseract-ocr/tesseract/build'
CMakeFiles/Makefile2:228: recipe for target 'src/training/CMakeFiles/text2image.dir/all' failed
make[1]: *** [src/training/CMakeFiles/text2image.dir/all] Error 2
make[1]: Leaving directory '/home/ubuntu/src/github/tesseract-ocr/tesseract/build'
Makefile:129: recipe for target 'all' failed
make: *** [all] Error 2

That looks like the linker does not get called with all necessary libraries.