message: linux-x86_64-config.jam cleanup
diff: import os ;
  using gcc : x86_64 : g++-7 :
  + <cxxflags>-std=c++17
  <cxxflags>-fPIC
  - <cxxflags>-std=c++14
  <cxxflags>-fno-strict-aliasing
  <cxxflags>-fvisibility=hidden
  + # debug information
  + <cxxflags>-g
  <linkflags>-static-libstdc++
  <linkflags>-static-libgcc
  <linkflags>"-z noexecstack"
  - # debug information
  - <cxxflags>-g
  - <cxxflags>-gdwarf-4
  - <cxxflags>-ggdb
  ;
  