D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
Actually, GDC supports shared libraries since version 6.2, but on Debian
there are still issues with that version due to the standard library not
being compiled with PIC.
Therefore, we make a very conservative assumption here and only enable
the tests for GDC >= 7.0
This allows us to disable the shared library test if the GNU D compiler
is detected.
This is useful, because gdc can not yet build proper shared libraries.
We also add a new test here which tests versioning of D shared
libraries.