Log Message:
some improvement
* Remove BUILD_DEPENDS on bison, it already in USE_TOOLS.
* Remove USE_BZIP2, not buildlink with bzip2, no effect.
* Remove custom do-* target, *_DIRS is sufficient to do so and use it instead.
* Remove MAKE_FLAGS="c c++", it was not used, and it result in missing \ 
"gcov"
  after above modification.
* then, add user-destdir support, inspired by PR 42438.