[ASan] Only run dlopen-mixed-c-cxx.c with static runtime

This is what the original bug (http://llvm.org/PR39641) and the fix
in https://reviews.llvm.org/D63877 have been about.
With the dynamic runtime the test only passes when the asan library
is linked against libstdc++: In contrast to libc++abi, it does not
implement __cxa_rethrow_primary_exception so the regex matches the
line saying that asan cannot intercept this function. Indeed, there
is no message that the runtime failed to intercept  __cxa_throw.

Differential Revision: https://reviews.llvm.org/D67298

llvm-svn: 371336