Not sure what the issue is, but it might be because the test copies
llvm-symbolizer to a different directory, and it can't find libc++.
Try to add some REQUIRES that we use in other tests where we copy
llvm tools out of their original directories.
We want way to set a path to llvm-symbolizer that isn't relative
to the current working directory; this change adds a variable that
expands to the path relative to the current binary.
This approach came from comments in https://reviews.llvm.org/D93070
Differential Revision: https://reviews.llvm.org/D94563
Amy Huang