[XVM] XVM framework and the implementation of dynamic library · Pull Request !479 · OpenHarmony/third_party_llvm-project

### Issue
A new LLVM backend for the secure language of XVM is required.
A pluggable mechanism is needed for separating the binary implementation of the XVM target with existing existing targets.

### Reason
This PR includes the LLVM XVM backend framework and the pluggable mechanism to make the XVM target as a pluggable target. All the work is based on the existing LLVM framework.

### Description

This PR has no effects on existing targets. It registers the new XVM target to be used in the toolchain.
When the input C code is asked to be compiled into the XVM code, it tries to look for the implementation of the XVM backend target, if not found, it issues the message of "unable to create target: 'No available targets are compatible with triple "xvm"';
Otherwise, it loads the XVM backend and compiles the input C code to the output XVM code.

### Test
Local tests on the targets of bpf and aarch64 are processed for testing that there is no effects on existing targets.
Local tests on the xvm target are processed for testing that proper error messages are issued.

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

- [y] yes，branch list:
- [ ] no
dev
master
2024_0416_llvm15_release
2024_0415_llvm15_release
2024_0315_llvm15_release
2023_0415_llvm15_release
2023_0415_llvm15_release_sp1
2023_0530_llvm15_release
2023_0630_llvm15_release
2023_0930_llvm15_release
2023_1130_llvm15_release
2023_1230_llvm15_release
2024_0103_llvm15_release
2024_0229_llvm15_release
2024_0130_llvm15_release

why:
It will be used by the teams who want to explore the XVM techniques.

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

Here is the URL of the corresponding issue:
https://gitee.com/openharmony/third_party_llvm-project/issues/I9MSPC?from=project-issue

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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