C++, testsuite: Adjust pure-virtual1.C options for Darwin.
Darwin's static linker expects, by default, that all linkage will
be satisfied (even for weak items). This allows the two-level
namespace to work even for weak cases.
However, there's an option to make it behave in a similar manner
to ELF. This is needed for the pure-virtual1.C testcase to pass
on Darwin.
gcc/testsuite/ChangeLog:
* g++.dg/abi/pure-virtual1.C: Add dynamic_lookup option
for Darwin.