d: Only test with default permutation flags for runnable tests.
Unless the test explicitly requests, all compilable tests as well as
fail_compilation tests will be ran without any extra flags.
The C++ tests now are checked against shared D runtime library.
gcc/testsuite/ChangeLog:
* lib/gdc-utils.exp (gdc-convert-test): Handle LINK directive.
Set PERMUTE_ARGS as DEFAULT_DFLAGS only for runnable tests.
(gdc-do-test): Set default action of compilable tests to compile.
Test SHARED_OPTION on runnable_cxx tests.