[CFI][clang][Driver][CodeGen] Introduce option to catch mixed CFI code · Pull Request !487 · OpenHarmony/third_party_llvm-project

### Issue
https://gitee.com/openharmony/third_party_llvm-project/issues/I9LG51

### Reason (Purpose, Solved Problem)
Currently in OpenHarmony builds some CFI-related issues are happening just because not all of the files participating in an LTO link are compiled with CFI enabled. AFAIU, this is better solved by the build system, but because still nothing was done, this can be supported from the toolchain side (with some drawbacks). In particular, this only works for [thin]LTO builds, where it is guaranteed that user code isn't linked into the LTO-enabled CFI build as ELF object files.

### Description
Introduce an option to check that all of the IR modules participating in the IR link have cross-DSO CFI enabled. Option should be specified to the compilation stage, and will fail the LTO link stage if all of the following conditions are met:
- all of the CFI-enabled modules were compiled with `-fsanitize-cfi-cross-dso-req` clang option
- at least one of the input IR modules was generated with `-fsanitize-cfi-cross-dso` (and so `-fsanitize-cfi-cross-dso-req`) clang options
- at least one of the input IR modules was generated without cross-DSO CFI.

Note that this doesn't catch CFI/cross-DSO CFI or non-LTO/any CFI code mixes.

Also, code compiled with `-fsanitize-cfi-cross-dso-req` is incompatible with code compiled without it, in the sense that the link stage won't fail as long as there is at least one module compiled with `-fsanitize-cfi-cross-dso -fno-sanitize-cfi-cross-dso-req`, so no errors would be detected.

### Test (Local test)

### Need to cherry-pick to release (eg：monthly_20221018, OpenHarmony-3.2-Beta5 ...) branch？

- [ ] yes，branch list:
- [x] no

why:

###  Compatibility impact assessment, please indicate (Y/N)

类型	指派人员	状态
审查	hhj Pavel Kosov 已审查通过	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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