[clang] [llvm] [RISCV][VLS] Support RISCV VLS calling convention (PR #100346)

[Kito Cheng via llvm-commits]

================
@@ -3013,6 +3013,7 @@ enum CXCallingConv {
   CXCallingConv_M68kRTD = 19,
   CXCallingConv_PreserveNone = 20,
   CXCallingConv_RISCVVectorCall = 21,
+  CXCallingConv_RISCVVLSCall = 22,
----------------
kito-cheng wrote:

Just use different calling convention to distinguish, then it would be easier to know the ABI_VLEN in the LLVM IR level, also can prevent the change in Type.h
```
CXCallingConv_RISCVVLSCall_32,
CXCallingConv_RISCVVLSCall_64,
...
CXCallingConv_RISCVVLSCall_65536,
```

https://github.com/llvm/llvm-project/pull/100346