CMake: Silence warnings about CMP0079

[dnakamura]

Tell newer versions of CMake that we expect the old behavior of CMP0079.

[dnakamura]

Eliminates a number of warnings of the form

CMake Warning (dev) at runtime/gc_glue_java/CMakeLists.txt:80 (target_link_libraries):
Policy CMP0079 is not set: target_link_libraries allows use with targets in
other directories.  Run "cmake --help-policy CMP0079" for policy details.
Use the cmake_policy command to set the policy and suppress this warning.

[pshipton]

jenkins compile all jdk8,jdk19