Implement vAttachOrWait

Implements the required functions on gdb-remote so the '--include-existing' flag of process attach works correctly on Linux.

Reviewed By: labath, clayborg

Differential Revision: https://reviews.llvm.org/D94672

GitOrigin-RevId: 2afaf072f5c1467767081571f2a3747b3ba91354
3 files changed