[lldb] Fix lldb stepping actions when receiving signals, part 1 · Pull Request !126 · OpenHarmony/third_party_llvm-project

## PR Description
Partially fixes issue(s):
- https://gitee.com/openharmony/third_party_llvm-project/issues/I64W4S
- A similar one, I65ADU (not linked because of gitee)

This is a preliminary patch that would fix lldb stepping actions (step-in, step-out, step-over, step-until and so on) when the app is receiving signals. When stepping off of a breakpoint, lldb needs to disable it first. To not miss anything, lldb disables the breakpoint, does a single-step (usually with `ptrace`) to the next instruction, enables the breakpoint again and considers it done. This breaks when a signal is received right after the breakpoint: program counter after the step (if the signal is handled by the current thread) ends up in a signal handler, and lldb thinks that we are done. When the program returns from the signal handler to the breakpoint, it is hit again. This manifests in the user having to step-* multiple times in a row to get progress, although the instruction under the breakpoint is only executed after the last step-*. This patch provides a simple solution to, while stepping off a breakpoint, set a breakpoint on the return address from a handler when a signal arrives, wait to hit it and then try again with single-stepping approach, until we are safely off the breakpoint. The downside is this creates inconsistencies with lldb behavior sometimes, see discussion comments on this PR. Tests will be merged as soon as possible in a subsequent PR.

It should be noted that this would work only if lldb is notified about the interrupting signals, which is by default not the case for real-time signals, which are a part of the original issue. So this patch in the specific case of #I64W4S works only if you run `process handle SIGRTMIN+1 -p true -s false -n true` (necessary) and `process handle SIGCHLD -p true -s false -n true` (just in case), all after the process has already been started (after a first breakpoint hit or after the process is stopped at entry).

类型	指派人员	状态
审查	hhj 已审查通过 Pavel Kosov	已完成 (1/1人)
测试	openharmony_ci 已测试通过	已完成 (1/1人)

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