Eliminate boilerplate of having each test manually assign to `mydir` by calling
`compute_mydir` in lldbtest.py.
Differential Revision: https://reviews.llvm.org/D128077
D120762 accidentally moved the interrupt check into the block which was
reading stdio. This meant that a ^C only took effect after a regular
character has been pressed.
This patch fixes that and adds a (pexpect) test.
Differential Revision: https://reviews.llvm.org/D121912
