report relevant env var behaviour to console
Several kinds of jobs / platforms / configurations rely on the environment variables having particular values. It would be good to report those on the console log for the benefit of people attempting to replicate them outside of Jenkins.
For example, while investigating #2162 it was harder to set up a static analysis build on a desktop than it would have been if there was a more visible clue that the analysis is supported by the way releng sets CCC_CC and CC_CXX.
The use (and reasons for use) of LD_LIBRARY_PATH, etc. could also be improved.Ideas:
- set_env_var echoes to the console (or fills a list that can be dumped before e.g. cmake call)
- clang-analyzer.py could use a different approach for setting the compiler (there are a few approaches supported by scan-build and c++-analyzer, not sure if others can work, however)
- echo reports about actions to manage compiler / toolchain / stdlib issues