[clang] [llvm] [RISCV] Implement the implications of C extension (PR #132259)

[Craig Topper via llvm-commits]

================
@@ -25,8 +25,8 @@ addi a0, a1, 0
 # CHECK: # encoding:  [0xe0,0x1f]
 addi s0, sp, 1020
 
-# CHECK: .option arch, -c
-.option arch, -c
+# CHECK: .option arch, -c, -zca
+.option arch, -c, -zca
----------------
topperc wrote:

The code for removing a feature doesn't even try to remove dependent features.

```
        assert(Type == RISCVOptionArchArgType::Minus);                           
        // It is invalid to disable an extension that there are other enabled    
        // extensions depend on it.                                              
        // TODO: Make use of RISCVISAInfo to handle this                         
        for (auto &Feature : RISCVFeatureKV) {                                   
          if (getSTI().hasFeature(Feature.Value) &&                              
              Feature.Implies.test(Ext->Value))                                  
            return Error(Loc, Twine("can't disable ") + Ext->Key +               
                                  " extension; " + Feature.Key +                 
                                  " extension requires " + Ext->Key +            
                                  " extension");
```

https://github.com/llvm/llvm-project/pull/132259