improved compiler selection, fix #1731
NEXT: 1.19.2 with 1731
separate --with-opt-dir= handling for rbx
Merge pull request #1782 from wayneeseguin/bugfix/rbx-head

separate --with-opt-dir= handling for rbx
NEXT: 1.19.2 with 1782
make sure /etc/bash.bashrc is set up properly, fix #1762
NEXT: 1.19.2 with 1762