FindBoost: added -clang{XX} compiler version
Added ability to search boost libraries built with clang. The prefix for those libs as follows -clang{version major minor here}
... lib/libboost_thread-clang50-mt-s-1_64.a lib/libboost_thread-clang50-mt-s-1_65_1.a lib/libboost_thread-clang50-mt-sd-1_64.a lib/libboost_thread-clang50-mt-sd-1_65_1.a ...
Note:
Current FindBoost.cmake removes old compiler check using -dumpversion.
For prior versions of the module, where -dumpverson used it will not work, because Clang will return "4.2.1"
Issue: #12940
Edited by Brad King