[msan] Add msan support for loongarch64

[tangyouling]

Summary

This patch enabled msan for loongarch64 with 47-bit VMA layout.

[XiaodongLoong]

ERROR   git-clang-format returned an non-zero exit code 1

Please format the code. Maybe, you can use the following command:

git diff -U0 --no-color HEAD^ | clang/tools/clang-format/clang-format-diff.py -i -p1

[tangyouling]

Add code format check.

[SixWeining]

compiler-rt/lib/msan/msan.h

192

We fall to this? But not line 208?

compiler-rt/test/msan/mmap.cpp

22–24

These addresses are the same as x86_64 above. Is this expected?

[tangyouling]

compiler-rt/lib/msan/msan.h

192

I will move the contents of line 208 to line 91.

compiler-rt/test/msan/mmap.cpp

22–24

Because the app-{1,2,3} definition of kMemoryLayout is consistent with x86_64, it is the same here.

[tangyouling]

Modify the kMemoryLayout definition position of loongarch64.

[SixWeining]

Seems that missing atest in llvm/test/Instrumentation/MemorySanitizer/.

[vitalybuka]

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

5879

it looks like exact copy of VarArgMIPS64Helper
why not "new VarArgMIPS64Helper"?

[tangyouling]

In D140528#4047132, @SixWeining wrote:

Seems that missing atest in llvm/test/Instrumentation/MemorySanitizer/.

Yes, need to add corresponding test for vararg.

[vitalybuka]

I assume work in progress