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
This is needed when mixing D and C code, as it's possible to end up
witha combination of linkers and compilres such that C produces pdb
files but D does not.
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.