Eliminate boilerplate of having each test manually assign to `mydir` by calling
`compute_mydir` in lldbtest.py.
Differential Revision: https://reviews.llvm.org/D128077
There was a little thinko which meant when stopped in a frame with
debug information but whose CU didn't have any global variables we
report:
no debug info for frame <N>
This patch fixes that error message to say the intended:
no global variables in current compile unit
<rdar://problem/69086361>